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Mixed Anion Exchange Resins for Tunable Control of SulfateChloride Selectivity for Sustainable Membrane Pretreatment Ryan Casey Smith, and Arup K. Sengupta Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b03081 • Publication Date (Web): 08 Jan 2016 Downloaded from http://pubs.acs.org on January 16, 2016

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Industrial & Engineering Chemistry Research

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Mixed Anion Exchange Resins for Tunable Control of Sulfate-Chloride Selectivity for

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Sustainable Membrane Pretreatment

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Ryan C. Smith and Arup K. SenGupta*

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Department of Civil and Environmental Engineering, Lehigh University, Bethlehem, PA 18015,

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USA

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*Corresponding author, email: [email protected], Tel: (610) 758-3534

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Abstract

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The recovery of water during inland desalination processes using reverse osmosis, or RO, is

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often limited by the solubility of calcium sulfate, or CaSO4. Reducing or eliminating the

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presence of sulfate from the feedwater will allow the process to be operated at higher recoveries

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and produce less waste brine. Ion exchange may be used as a pretreatment method for the control

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and removal of sulfate using a hybrid ion exchange-reverse osmosis (HIX-RO) process.

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However, for viable application, it is imperative that the process is self-regenerating i.e., the use

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of external regenerants has to be avoided altogether. Various properties of the ion exchange resin

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control the overall selectivity toward sulfate including the resin matrix and basicity of the

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functional group. Finer control over selectivity is also possible through mixing of

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characteristically different ion exchange resins. This study focused on how mixing of anion

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exchange resins with different matrix and functional groups may optimize sulfate/chloride

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selectivity avoiding precipitation of CaSO4 for a specific brackish. Finally, lab-scale results from

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an HIX-RO system are presented demonstrating higher RO recovery with no need for an external

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regenerant.

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Introduction

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Various processes are used for the desalination of saline water: reverse osmosis (RO), multi-

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stage flash distillation, electrodialysis, etc. Yet, regardless of the desalination method practiced,

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the byproduct of desalination is concentrated saline brine that must be properly

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disposed/discharged into the surrounding environment. For coastal desalination processes, waste

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brine is usually discharged back into the ocean. However, for inland desalination processes, there

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is no easy method of brine disposal and different methods of concentrate management must be

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considered; the most common methods being deep well injection, evaporation ponds, or zero

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liquid discharge systems.1-5 The costs associated with concentrate management vary widely

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depending on the type of water being treated, the physical location of the treatment plant, and

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local laws regarding discharge, but for some inland brackish water desalination plants the costs

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associated with disposal are nearly 50% of the plant operating costs.6 No matter what method of

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concentrate disposal is practiced, there is a potential for cost savings by decreasing the volume of

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concentrate produced: the smaller is the volume of saline brine discharged, the lower is the

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overall cost of disposal.

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Decreasing the volume of produced concentrate is only possible by increasing the

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recovery of the desalination process. This is not immediately attainable since at higher recoveries

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there is increased potential for scale formation due to precipitation; some of the most common

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precipitates being carbonate salts like calcite (CaCO3) or sulfate salts like gypsum

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(CaSO4·2H2O) or barite (BaSO4).7,8 Sulfate salts, unlike carbonate salts, are unaffected by acid

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dosing and cannot be completely prevented but only inhibited through the use of anti-scaling

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agents.9 Current studies on preventing or inhibiting gypsum scaling have mostly focused on two


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stage RO processes which have an intermediate step where precipitation is induced in the RO

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concentrate.10-13

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A unique pretreatment system may be designed where the influent sulfate is removed by

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ion exchange and replaced by chloride before desalination. Ion exchange resins show high

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affinity toward sulfate even in the presence of background ions. The selective removal and

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replacement of sulfate by chloride would completely eliminate any threat to scaling since salts of

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chloride are orders of magnitude more soluble than those of sulfate. The solution exiting the ion

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exchange column would have significantly lower scaling potential, and the desalination process

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could be operated at higher recoveries.

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Eventually, the resin will need to be regenerated; this is normally accomplished by

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passing prepared concentrated brine. However, from a sustainability viewpoint, such an approach

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of adding external chemicals is undesirable and also, the additional cost and operational

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complexity reduces the value of the proposed approach. Instead, use of the reject brine from the

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RO unit as the sole regenerant, if at all possible, offers the opportunity for a holistic process that

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improves the product water recovery eliminating the need for an externally added chemical as a

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regenerant.

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Depicted in Figure 1A is a normally operating RO system that is unable to prevent the

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formation of CaSO4 scaling. The potential for sulfate scaling during RO is dictated by the ion

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activity product (IAP) between Ca2+ and SO42-. When the IAP exceeds the solubility product,

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Ksp, calcium sulfate scaling is thermodynamically favorable.14 By using ion exchange to remove

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and replace sulfate with chloride, Figure 1B, the IAP may be reduced below Ksp preventing the

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formation of CaSO4 scaling.

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Figure 1. (A) Formation of CaSO4 due to high recovery and no removal of sulfate (B) Effective

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removal of sulfate using ion exchange pretreatment and elimination of CaSO4 scaling

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In order for the process to be sustainable, sulfate must be selectively removed from the feedwater

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by the resin before the RO unit, and then displaced by chloride during regeneration using the RO

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reject. Achieving this goal is not immediately apparent as there are several factors which can

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affect and change ion exchange affinity. Wide variability in the composition of various

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feedwaters means that achieving this goal may not be possible with a single commercially

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available ion exchange resin. To this end, we attempt to demonstrate that by mixing

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characteristically different resins, finer control over sulfate selectivity is possible. One previous

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study demonstrated that a hybrid ion exchange-reverse osmosis (HIX-RO) process is capable of

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reducing the volume of reject and thus, alleviate the concentrate brine disposal problem

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confronted with inland desalination.15 Hybrid ion exchange-desalination processes have been

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studied in the past, but these were mainly focused on the removal of boron from seawater.16

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The broad objective of this communication is to present and demonstrate that different

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properties of anion exchange resins will influence sulfate selectivity and therefore the overall 4 ACS Paragon Plus Environment

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sustainability of the HIX-RO process. Furthermore, we show evidence that precise control over

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sulfate selectivity is possible by mixing together commercially available anion exchange resins

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in a calculated proportion.

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Scientific Challenges and Objectives

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The uptake of sulfate by an ion exchange resin loaded with chloride follows Reaction 1: 2R N Cl + SO → R N SO + 2Cl

Rxn. 1

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Where overbar represents the solid phase ion exchanger and R4N+ is the functional group of the

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ion exchange resin. Note that this is heterovalent ion exchange i.e., exchanging couterions, SO42-

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and Cl-, have unequal charges. The equilibrium constant, K, for an ion exchange reaction under

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ideal conditions is known as the selectivity coefficient, and for Reaction 1 between sulfate and

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chloride, KS/Cl is expressed as17 / =

Eq. 1

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In which x is the fraction of sulfate or chloride in solution and y is the fraction of sulfate or

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chloride on the resin. CT is the total concentration of ions in solution, in meq/L, and Q is the resin

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capacity, in meq/g. Supporting Information Section S1 provides the derivation of Equation 1.

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At a given temperature, KS/Cl is an inherent property of the resin. The relative ion exchange

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affinity of one ion compared to another is known as the separation factor, α, and for sulfate and

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chloride αS/Cl is provided as

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/ =

Eq. 2 5

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Contrary to KS/Cl, αS/Cl is not a constant. When αS/Cl > 1 sulfate is the preferred species and vice

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versa. For heterovalent ion exchange, αS/Cl is dependent on both CT and the resin composition.17-

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20

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For the HIX-RO process in Figure 1B, the resin capacity for Rxn. 1 will eventually be

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exhausted and must be regenerated with a solution rich in chloride concentration. Sulfate is

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removed from the resin and replaced by chloride using a concentrated sodium chloride or brine,

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and for the proposed HIX-RO process this would be from the reject stream from the RO unit.

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Regeneration follows the following reaction: R N SO + 2Cl → 2R N Cl + SO

Rxn. 2

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In order for the resin to be efficiently regenerated, αS/Cl must be less than unity, that is, the same

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anion exchange resin would have to prefer chloride over sulfate. Thus, in Figure 1B, Column 1

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and Column 2 switch during the process from brackish water influent to RO reject and their

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sulfate/chloride selectivity must reverse to sustain the proposed process without needing any

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external regenerant. Obviously, the challenge lies in identifying appropriate anion exchange resin

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for a specific brackish water composition to satisfy the foregoing criterion.

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Control of αS/Cl through bulk resin properties

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For anion exchange resins, matrix and functional groups are the primary composition variables

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influencing affinity toward exchanging anions. Thus, for sulfate/chloride exchange, the

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separation factor /), is dependent on the matrix type and the basicity of the functional

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group; several previous studies have addressed this subject.21-24


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Matrix type refers to the base polymer that has been functionalized to give ion exchange

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capabilities; the two most commonly available commercial polymers are polystyrene and

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polyacrylate. Because of its greater hydrophilicity, polyacrylate resins are more sulfate selective

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than polystyrene, all other conditions remaining identical. Basicity is a measure of the pKa of the

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amine functional group; a lower pKa results in higher sulfate selectivity.25 By varying either the

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matrix type or the basicity, broad control over αS/Cl is possible; these effects are summarized in

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Figure 2.

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Figure 2. An illustration of the effect of resin matrix and functional group on overall

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sulfate/chloride selectivity

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Varying bulk resin properties allows for broad control over the selectivity coefficient, and has

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been shown to be an effective method for the selective removal of trace contaminant ions.26

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However, for the proposed HIX-RO process both the feedwater and RO reject concentrations are

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fixed. Since only a certain range of αS/Cl values will allow the process to operate, more fine-



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tuning is required. For these cases, greater control over αS/Cl can be obtained through mixing of

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two characteristically different resins.

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Control of αS/Cl through resin mixing

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When mixing two different ion exchange resins “A” and “B” together in a plug-flow column, the

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fraction of the column that is resin A, ΦA, may be calculated by

148 +

Eq. 3

= 1 − +

Eq. 4

= 149 150

Similarly for resin B

151 = 152 153 154 155

Where mA and mB represent the masses of respective resins. The total capacity of the ion exchange column, Q*, is calculated from the capacity of the individual resins QA and QB and resin fraction ΦA ∗ = + 1 −

Eq. 5

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Calculation of the overall column separation factor, α*S/Cl, is similar to Eq. 2 and calculated by

∗

/ =

∗ ∗

Eq. 6

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In which y* is the overall fraction of the column in either sulfate or chloride form and is

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calculated by 8 ACS Paragon Plus Environment

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∗ =

+ 1 − ∗

Eq. 7

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It is important to note that α*S/Cl is the overall column separation factor. For the individual ion

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exchange resins, αS/Cl has not changed but when two different resins with different αS/Cl values

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are mixed the overall column separation factor is changed and dependent on the mixing

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ratio of the resins.

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A series of experiments were carried out with both anion exchange resins and the HIX-

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RO process using brackish water of varying composition.15 Specific objectives of this

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communication are to validate that: i) Sulfate/chloride separation factor can be modified by

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mixing anion exchange resins of different compositions; ii) the mixing ratio of two anion

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exchange resins can be appropriately tuned to attain α*S/Cl >1.0 for a specific feed water and

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α*S/Cl < 1.0 for the RO reject water with sulfate-chloride selectivity reversal; iii) the HIX-RO

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process is self-regenerating and can be operated using brackish feed waters with no possibility of

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CaSO4 precipitation and requiring no external regenerant.

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Materials and Methods

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Ion Exchange Resins

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Two strong base anion exchange resins were used throughout this study a polystyrene resin. IRA

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900, and a polyacrylate resin, A850. Individual resin properties are detailed in Table 1.

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Table 1. Properties of anion exchange resins used in this study Trade Name Manufacturer Resin Type Matrix

A400 Purolite Strong base Polystyrene

IRA 900 Rohm and Haas Co. Strong base Polyacrylate



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Resin properties such as selectivity and capacity were determined experimentally.

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Determination of αS/Cl Using Batch Isotherms

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Before running isotherms, resins were first converted into chloride form. Resin was packed in a

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1.1 cm diameter glass column with glass wool supports and a solution of 0.1 M sodium chloride

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was passed at 2 mL/min using a ceramic piston pump until the influent and effluent chloride

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concentrations were equal. The column was then washed with deionized water. After

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conditioning, resin was removed from the glass column and left to air dry at room temperature.

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For each batch isotherm, a stock solution of 30 meq/L, 80 meq/L, or 150 meq/L sodium

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sulfate was prepared and 50 mL aliquots were placed in Nalgene bottles along with varying

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masses of air-dried resin. The bottles were capped, sealed with Parafilm, and placed on a rotary

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shaker for at least 24 hours and kept at 23 ± 2 °C. Supernatant was decanted from the resin and

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the solution composition was analyzed.

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Measuring Resin Capacity

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Resin capacity was measuring by placing a known mass of air dried resin in chloride form in a

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glass column. A dilute solution of sulfate was passed and the effluent solution was collected in a

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glass beaker. The column was run until influent and effluent sulfate concentrations were equal.

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Capacity was determined by measuring the total mass of chloride in the effluent solution which

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was then assumed to be the total mass of chloride present on the column, and therefore the resin

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capacity.

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HIX-RO Runs

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Lab-scale investigations on the efficacy of using ion exchange as a pretreatment for RO were

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performed using a feedwater based on representative brackish water composition from the San

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Joaquin Valley, CA and other locations. Figure 3 shows the general arrangement of the HIX-RO

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laboratory set-up used in the study. Ten cycles of HIX-RO were performed using a i) a mixture

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of 1L mixture of polystyrene and polyacrylic resin and ii) individual resins. For each cycle, 20 L

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of prepared feedwater was passed through the 1 L ion exchange column and collected. The

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effluent was subjected to reverse osmosis using a Dow Filmtec SW30-2540 RO membrane.

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Solution in the feed tank was kept at 20 °C ± 2 °C by submersing a cooling coil into the tank.

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Transmembrane pressure ranged from 44-46 atm and was adjusted to ensure 80% permeate

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recovery. Permeate flux was, on average, between 35 L/m2-hr and 45 L/m2-hr. The produced

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concentrate brine was used as the regenerant for the ion exchange column; no additional

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chemicals were used. In between cycles, the ion exchange column was not washed or disturbed

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in any way; only feedwater and RO concentrate were passed through the ion exchange column.

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Figure 3. Laboratory setup used for all HIX-RO runs performed

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Sample Analyses

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Chloride concentration was determined by titration with silver nitrate using a potassium

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chromate indicator, and sulfate was analyzed using a Hach spectrophotometer (Model #DR

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5000) and SulfaVer 4 testing kit (Hach Company, Loveland, CO).27

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Scanning Electron Microscopy and Energy Dispersive X-Ray (EDX) Scanning

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Resin beads were first washed with deionized water and left to air dry. Individual beads were

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held using a set of fine tweezers and sliced in half using a razor blade dipped in liquid nitrogen.

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The sliced beads were then mounted on pegs using double-sided carbon tape and sputter coated

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with iridium using an Electron Microscopy Sciences high vacuum sputter coater (Model


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EMS575X). Scanning Electron Microscopy (SEM) was performed on resin beads using a Zeiss

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1550 Field Emission Scanning Electron Microscope equipped with an EDX system from INCA

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used for mapping and analysis.

235 236

Results and Discussion

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Effect of resin matrix on αS/Cl

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First studied was the effect of resin matrix on overall sulfate selectivity. Six batch studies were

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performed using both a strong base polyacrylic and a strong base polystyrene resin at 80 meq/L

240

total ion concentration. The resulting equilibrium values and isotherm curves generated from

241

these batch tests is shown in Figure 4.

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Figure 4. Batch equilibrium isotherms for strong-base polystyrene and strong-base polyacrylic

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resin at CT = 80 meq/L. Dashed lines indicate the fitted curve using Equation 8.

245



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The fraction of sulfate on the resin is given by yS and the fraction of sulfate in solution is xS. The

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separation factor, αS/Cl, for each resin was determined by Eq. 8.22

248 − − ln / − 1 Area below isotherm = Area above isotherm 1 − − − ln / − 1

Eq. 8

249 250

The areas above and below the isotherm were calculated using the trapezoid rule and solving Eq.

251

8 for αS/Cl. From the measured data and using Eq. 1, KS/Cl values were also calculated. Table 2

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summarizes the pure resin parameters.

253 254

Table 2. Measured pure resin parameters from batch isotherm studies Polyacrylic 2.2 Q (meq/g dry resin) 2.36 αS/Cl at 80 meq/L 114.9 KS/Cl (g/L)

Polystyrene 3.628 0.35 6.47

255 256

Comparing resin matrix effects only, the polyacrylic resin shows significantly higher affinity

257

toward sulfate than the polystyrene resin. This is reflected in the lower KS/Cl value for the

258

polystyrene resin compared to the polyacrylic resin. The measured αS/Cl values are only valid at

259

this CT while KS/Cl remains constant regardless of experimental conditions.

260 261

Effect of functional group basicity on αS/Cl

262

In order to determine the effect of basicity on sulfate selectivity, three strong base polyacrylic

263

anion exchange resins with difference basicities were considered: a mixed primary amine resin

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with an indeterminate mixture of both secondary and primary amines, a tertiary amine resin, and

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the same quaternary amine resin listed in Table 2. Resin properties like KS/Cl and Q for the 14 ACS Paragon Plus Environment

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mixed primary resin were previously published,29,30 and resin data for the tertiary amine resin

267

was garnered from open literature.23. The effect of the basicity of an ion exchange resin on αS/Cl

268

is best demonstrated by plotting the change in αS/Cl with CT. This is accomplished by using the

269

fixed values of KS/Cl and Q to calculate αS/Cl from Eq. 1. These results are plotted in Figure 5

270

which also indicates the predicted CT value at which αS/Cl = 1.0 i.e., the point of selectivity

271

reversal.

272

273 274

Figure 5. Effects of total electrolyte concentration (CT) and basicity of the anion exchanger

275

functional group.

276 277

Note that both axes in Figure 5 are log scale. Of particular interest is the CT value at which αS/Cl

278

crosses from greater than 1 to less than 1. This transition is known as selectivity reversal and 15 ACS Paragon Plus Environment


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indicates when the resin begins to selectively remove chloride, a monovalent species,

280

preferentially over sulfate, a divalent species.

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Every time a methyl group is removed, the point of selectivity reversal increases by

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approximately one order of magnitude. The order of selectivity reversal and the general trend of

283

the system follows:

284

Primary/Secondary > Tertiary > Quaternary

285

For HIX-RO, there may be a large difference in CT values between the feedwater and the RO

286

reject. For instance, if the desalination process were to be operated at 90% recovery, the reject

287

stream would be one order of magnitude more concentrated than the feedwater.

288 289

Mixed Resin Isotherms

290

Figures 4 and 5 demonstrate that sulfate/chloride separation factor value or αS/Cl is dependent on

291

both resin matrix and the basicity of the functional group. However, for every brackish water

292

composition, it is nearly impossible to identify a single anion exchange resin that will exhibit

293

sulfate-chloride selectivity reversal between the feed and the reject water during the RO process

294

i.e., αS/Cl is greater at the feedwater CT and less than one at RO reject CT. Finer control may thus

295

be necessary if the point of selectivity reversal does not fall between feedwater and RO reject

296

concentrations. Since both the feedwater and RO concentrate are fixed in concentration, an

297

optimum mixing of different anion exchange resins may be an effective method of precisely

298

controlling the range of αS/Cl.

299

For example, brackish water in Hueneme, California has a total influent concentration of

300

30 meq/L.3 If the water were to be desalinated at 80% recovery, the concentrate stream from the

301

RO would have a total concentration of 150 meq/L. Using the selectivity data from Table 2 to


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theoretically calculate αS/Cl, neither the polyacrylic resin nor the polystyrene resin have the

303

desired values of αS/Cl at 30 meq/L and 150 meq/L (Supporting Information Section S2).

304

However, predictions show that a 50/50 of the two resins will result in the desired range of α*S/Cl

305

values (Supporting Information Section S3). To this end, batch isotherms were performed

306

using a 50/50 mixture of polystyrene and polyacrylic resins and the results are plotted in Figure

307

6.

308 309

Figure 6. Comparison between theoretically predicted α*S/Cl and experimentally determined

310

α*S/Cl for 50/50 mixture of polystyrene/polyacrylic resin at 30 meq/L and 150 meq/L

311 312

There are two important observations that can be drawn from Figure 6. First, αS/Cl is greater than

313

one at 30 meq/L and less than one at 150 meq/L, as desired for a self-regenerating HIX-RO

314

process. Second, the experimental data points from sulfate-chloride equilibrium were found to be

315

in good agreement with the theoretically predicted isotherms at both 30 meq/L and 150 meq/L.



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This observation offers compelling evidence that α*S/Cl can be accurately predicted for a mixture

317

of resins only from knowing the individual resin properties through KS/Cl and Q.

318

The overall range of possible α*S/Cl values can be depicted by plotting calculated values

319

of α*S/Cl as total concentration, CT, and the mixing ratio, ΦA, change as shown in Figure 7; note

320

that the range of α*S/Cl values is in log scale. For any CT value, by changing the mixing ratio of

321

the two resins there is, on average, about one order of magnitude difference in α*S/Cl values.

322

323 324

Figure 7. Theoretical variation in α*S/Cl with different CT and mixing ratio, ΦA with open circles

325

demonstrating experimental validation for two different CT isotherms

326


Page 19 of 31

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327

Also plotted in Figure 7 are the experimentally determined α*S/Cl values from Figure 6 and two

328

thick lines at 30 meq/L and 150 meq/L showing what range of mixing ratios resulting in α*S/Cl

329

being greater than unity at 30 meq/L and less than unity at 150 meq/L. Color shading allows

330

quick determination of the value of α*S/Cl and therefore the point of selectivity reversal between

331

two concentration ranges for different mixing ratios.

332

For the two resins studied, the range of viable ΦA values is 0.2 to 0.7; note that this range

333

does not include ΦA = 1 or ΦA = 0 i.e. neither of the pure resins will work for the HIX-RO

334

process and therefore mixing is required for this feedwater composition. Also, the experimentally

335

determined α*S/Cl values at 30 meq/L and 150 meq/L for ΦA = 0.5 are superimposed on the

336

figure (shown by white circles), and they demonstrate good agreement with theoretically

337

determined α*S/Cl values thereby demonstrating the usefulness of the plot for other CT and ΦA

338

values.

339 340

HIX-RO Runs: Reversibility and Saturation Index (SI)

341

In order to validate the possibility of using mixed anion exchange resins for sulfate control

342

during brackish water desalination with HIX-RO process, we synthesized a brackish water

343

similar to that in San Joaquin Valley, CA. This brackish water has been investigated earlier for

344

RO processes primarily due to its propensity to precipitate CaSO4 at membrane surfaces with an

345

increase in product water recovery.15 Figure 8 illustrates the gradual build-up and eventual

346

supersaturation of CaSO4 for RO processes with an increase in recovery; the brackish water

347

composition is also included in Figure 8. The ordinate in the figure represents saturation index

348

(SI) of calcium sulfate and is calculated using OLI Stream Analyzer software using Equation

349

9.31



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

SI =

4Ca 54SO 5 67

Page 20 of 31

Eq. 9

350 351

Where Ksp is the thermodynamic solubulity product of CaSO4(s). Note that at about 50%

352

recovery, the SI for CaSO4 is nearly equal to unity. Should sulfate concentration in the feed be

353

reduced by 80% and replaced by equivalent amount of chloride, percentage recovery can exceed

354

well over 80% while the SI value for CaSO4 still remains under unity. The challenge remains in

355

sustaining such sulfate removal process without externally added chemicals.

356

357 358

Figure 8. Variation in calcium sulfate saturation index with increasing recovery of RO process

359 360

Ten cycles of HIX-RO processes were carried out separately using two different sets of anion

361

exchange resins: One with pure (ΦA = 0) polystyrene matrix, and the second with 50-50 mixture 20 ACS Paragon Plus Environment

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362

(ΦA = 0.5) of polystyrene and polyacrylic matrix. Figure 9A shows that in both cases, the quality

363

of the treated water (plot of conductivity versus cycle) remained nearly the same i.e., the

364

composition of the treated water was not influenced by the composition of the anion exchange

365

resin used in the HIX-RO process. Figures 9B and 9C present experimentally determined

366

CaSO4 SI values of the concentrate and the corresponding sulfate concentrations for both ΦA = 0

367

(pure resin) and ΦA = 0.5 (mixed resin), respectively. Note from Figure 9B that for the 50-50

368

mixed resin, CaSO4 SI value was consistently less than 1.0 during the course of 10 cycles, thus

369

eliminating any possibility of CaSO4 scaling. On the contrary, the pure polystyrene matrix resin

370

(ΦA = 0) exhibits SI values close to 2.0 for most of the cycles confirming the possibility of scale

371

formation at the membrane interface. Figure 9C shows that much higher sulfate removal by the

372

mixed resin compared with the pure resin is the primary reason for attaining an SI value

373

significantly lower than unity. This observation is consistent with the self-regeneration of the

374

mixed bed as predicted from the reversibility of the sulfate-chloride separation factor value

375

(α*S/Cl) from the service to the regeneration cycle. Although not presented here for the sake of

376

brevity, the performance of the pure resin with polyacrylic matrix was also inferior to that of the

377

mixed resin during HIX-RO cycles.

378



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Page 22 of 31

379 380

Figure 9. (A) Permeate conductivity for cycle (B) CaSO4 saturation index for both pure

381

polystyrene and mixed resin bed (C) Percent removal of sulfate for both pure polystyrene and

382

mixed resin bed

383 384

An Autopsy of the Resin Beads

385

Sulfate removed from the brackish feedwater during the forward pass prevents supersaturation

386

and potential scaling of CaSO4 onto the RO membrane. During the reverse pass, sulfate is

387

desorbed by RO reject and sulfate concentration in the exiting stream is significantly greater than

388

that in the feed. However, this stream of concentrate only goes to waste and is never in direct

389

contact with RO membrane. Nevertheless, in-column precipitation is thermodynamically feasible

390

because the saturation index is greater than unity. Following the procedure outlined in

391

Supporting Information Section S4, HIX-RO runs were carried out using a small-scale ion


Page 23 of 31

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392

exchange column using the same feedwater and mixed (ΦA = 0.5) resin for 10-minute contact

393

time.

394

Three consecutive cycles were run with synthetic RO concentrate corresponding to 80%

395

recovery from San Joaquin Valley water and no precipitates were observed within the mixed

396

anion exchange column. Precipitation of CaSO4 inside the ion exchange column would only

397

occur when the induction time of CaSO4 was below the 10 minute empty bed contact time; other

398

researchers have shown that even at an SI value of ~4.5, well above the studied value of 2.5,

399

greater than 13 minutes of induction time is required before CaSO4 precipitation is seen.32

400

White CaSO4 precipitates were formed in the collected effluent solution nearly 120

401

minutes after exiting from the column. Sulfate concentration inside the gel phase of the anion

402

exchange resins is significantly greater than in the aqueous phase in the interspaces between the

403

resin beads. Thus, CaSO4 precipitation is most likely to occur within the resin bead and any

404

evidence of the presence or absence of calcium inside the beads is of paramount significance. A

405

few resin beads from the column during the reverse pass were collected, sliced and characterized

406

through SEM-EDX technique with mapping. Figure 10A shows the SEM mapping of different

407

elements while Figure 10B provides SEM-EDX intensity peaks of different elements. Note that

408

Cl, S and O are significantly present. While Cl- is the source of Cl peaks, S and O are due to the

409

presence of sulfate (SO42-) inside the anion resin. A small Na peak is also present but Ca is

410

completely absent confirming the absence of CaSO4 in the gel phase i.e., no precipitation of

411

CaSO4 within the ion exchange resin beads. It is postulated that the Donnan exclusion effect did

412

not allow any permeation of Ca2+ within the anion exchanger.33

413



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Page 24 of 31

414 415

Figure 10. (A) SEM mapping of sliced resin bead (B) Mapping of resin bead showing relative

416

amounts of each element with no presence of calcium

417 418

Concluding Remarks

419

Ion exchange processes require regeneration and the disposal of spent regenerant often, if not

420

always, poses a major problem. Desalination by RO membrane processes often suffers from

421

irreversible scaling and consequent fouling of RO membranes due to the precipitation of poorly

422

soluble salts, namely, calcium sulfate. In this study, we present a synergy between the anion

423

exchange and the RO process where no external regenerant is necessary and the precipitation of

424

calcium sulfate can be completely avoided even with an increase in product water recovery. In

425

the past, researchers tried to use cation exchange resins to avoid precipitation by controlling

426

Ca/Na selectivity while achieving self-regeneration.34-43 However, that goal has not been

427

achieved as yet. Commercially available anion exchange resins have appropriate composition

428

variables, namely, functional group, matrix and basicity to tailor sulfate/chloride selectivity as

429

needed. In this research, a mixed bed of anion exchange resins have been used for the first time

430

to achieve the desired goal. The key findings of the research may be summarized as follows: 24 ACS Paragon Plus Environment

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431


•

A 50-50 mixture of two anion exchange resins with different matricies (polyacrylic and

432

polystyrene) allowed complete reversibility during the HIX-RO process with

433

dimensionless saturation index of CaSO4 in the concentrate less than unity.

434

•

By changing the mixing ratio of the two resins, the reversibility can be attained for a

435

broader range of brackish water concentrations (Figure 7) i.e., the proposed process is

436

flexible in its application for a wide variety of brackish water compositions.

437

•

Based on the selectivity coefficient data of commercial anion exchange resins already

438

available, a theoretical model may easily be developed to formulate the optimum

439

composition of the mixed bed for a given brackish water composition.

440

•

The overall sustainability of the inland brackish water desalination can be greatly

441

enhanced by integrating self-regenerating anion exchange process in tandem with RO

442

process with lower volume of concentrate needing disposal.

443 444

Supporting Information

445

A derivation of Equation 1, an explanation for the calculation of individual resin αS/Cl values at

446

30 meq/L and 150 meq/L and the overall mixed α*S/Cl values, and the procedure for the small

447

scale in-column precipitation study.

448 449

Acknowledgements

450

This research was funded by a grant from the National Science Foundation Accelerating

451

Innovation Research Grant (NSF-AIR #1311758) and the Pennsylvania Infrastructure

452

Technology Alliance (PITA).

453 25 ACS Paragon Plus Environment


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454 455

Page 26 of 31

References (1)

Xu, P.; Cath, T. Y.; Robertson, A. P.; Reinhard, M.; Leckie, J. O.; Drewes, J. E. Critical

456

Review of Desalination Concentrate Management, Treatment and Beneficial Use. Environ. Eng.

457

Sci. 2013, 30, 502–514.

458

(2)

Pérez-González, A; Urtiaga, A.M.; Ibáñez, R.; Ortiz, I. State of the Art and Review on

459

the Treatment Technologies of Water Reverse Osmosis Concentrates. Water Res. 2012, 46, 267–

460

283.

461

(3)

Greenlee, L. F.; Lawler, D. F.; Freeman, B. D.; Marrot, B.; Moulin, P. Reverse Osmosis

462

Desalination: Water Sources, Technology, and Today’s Challenges. Water Res. 2009, 43, 2317–

463

2348.

464

(4)

Mickley, M.C. Desalination and Water Purification Research and Development Program

465

Report No. 155. Treatment of Concentrate; US Department of the Interior Bureau of

466

Reclamation. May 2009.

467 468 469 470 471

(5)

Younos, T. Environmental Issues of Desalination. J. Contemp. Wat. Res. & Educ. 2005,

132, 11-18. (6)

National Research Council. Desalination: A National Perspective; The National

Academies Press: Washington, DC, 2008. (7)

Shih, W.-Y.; Rahardianto, A.; Lee, R.W.; Cohen, Y. Morphometric Characterization of

472

Calcium Sulfate Dihydrate (gypsum) Scale on Reverse Osmosis Membranes. J. Membr. Sci.

473

2005, 252, 253–263.

474

(8)

Alhseinat, E.; Sheikholeslami, R. An Application for New Reliable Approach to Predict

475

the Onset of Barite, Celestite and Gypsum Scaling during Reverse Osmosis Treatment for

476

Produced Water. Int. J. Environ. Sci. Dev. 2011, 2 (6), 454-459. 26 ACS Paragon Plus Environment

Page 27 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

477


(9)

McCool, B. C.; Rahardianto, A.; Faria, J.; Kovac, K.; Lara, D.; Cohen, Y. Feasibility of

478

Reverse Osmosis Desalination of Brackish Agricultural Drainage Water in the San Joaquin

479

Valley. Desalination 2010, 261, 240–250.

480

(10) Halevy, S.; Korin, E.; Gilron, J.; Kinetics of Gypsum Precipitation for Designing

481

Interstage Crystallizers for Concentrate in High Recovery Reverse Osmosis. Ind. Eng. Chem.

482

Res. 2013, 52, 14647-14657.

483

(11) McCool, B. C.; Rahardianto, A.; Cohen, Y. Antiscalant Removal in Accelerated

484

Desupersaturation of RO Concentrate via Chemically-Enhanced Seeded Precipitation (CESP).

485

Water Res. 2012, 46, 4261-4271.

486

(12) Greenlee, L. F.; Testa, F.; Lawler, D. F.; Freeman, B. D.; Moulin, P. Effect of antiscalant

487

degradation on salt precipitation and solid/liquid separation of RO concentrate. J. Mem. Sci.

488

2011, 366, 48-61.

489

(13) Comstock, S.E.H.; Boyer, T.H.; Graf, K.C. Treatment of nanofiltration and reverse

490

osmosis concentrates: Comparison of precipitative softening, coagulation, and anion exchange.

491

Wat. Res. 2011, 45, 4855-4865.

492

(14) Stumm, W.; Morgan, J.J. Aquatic Chemistry; John Wiley & Sons, Inc.: New York, 1996.

493

(15) Smith, R.C.; Sengupta, A.K. Integrating tunable anion exchange with reverse osmosis for

494

enhanced recovery during inland brackish water desalination. Environ. Sci. Technol. 2015, 49

495

(9), 5637-5644.

496

(16) Kabay, N.; Köseoğlu, P.; Yapıcı, D.; Yüksel, Ü.; Yüksel, M. Coupling ion exchange with

497

ultrafiltration for boron removal from geothermal water-investigation of process parameters and

498

recycle tests. Desalination. 2013, 316, 17-22.

499

(17) Helfferich, F. G. Ion Exchange; Dover Publications, Inc.: New York, 1995.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

500 501 502 503 504 505

(18) Li, P.; SenGupta, A. K. Genesis of selectivity and reversibility for sorption of synthetic aromatic anions onto polymeric sorbents. Environ. Sci. Technol. 1998, 32(23), 3756-3766. (19) Li, P.; SenGupta, A. K. Intraparticle Diffusion during Selective Ion Exchange with a Macroporous Exchanger. React. Funct. Polym. 2000, 44, 273. (20) Li, P.; SenGupta, A. K. Sorption of hydrophobic ionizable organic compounds (HIOCs) onto polymeric ion exchangers. React. Funct. Polym. 2004, 60, 27-39.

506

(21) Guter, G.A. Nitrate Removal from Contaminated Groundwater by Anion Exchange. In

507

Ion Exchange Technology: Advances in Pollution Control; SenGupta, A.K., Ed.; Technomic

508

Publishing Co. Inc.: Lancaster, PA, 1995; pp 61-148.

509 510 511 512

Page 28 of 31

(22) Clifford, D.; Weber Jr., W.J. The determinants of divalent/monovalent selectivity in anion exchangers. React. Polym. 1983, 1, 77-89 (23) Boari, G.; Liberti, L.; Merli, C.; Passino, R. Exchange equilibria on anion resins. Desalination 1974, 15, 145-166.

513

(24) Bonnesen, P.V.; Brown, G.M.; Alexandratos, S.D.; Bavoux, L.B.; Presley, D.J.; Patel, V.;

514

Ober, R.; Moyer, B.A. Development of bifunctional anion-exchange resins with improved

515

selectivity and sorptive kinetics for pertechnetate: batch-equilibrium experiments. Environ. Sci.

516

Technol. 2000, 34, 3761-3766.

517

(25) Smith, R.C. Integrating tunable anion exchange with reverse osmosis for enhanced

518

recovery during inland brackish water desalination. Ph.D. Dissertation, Lehigh University,

519

Bethlehem, PA, 2015.

520 521

(26) Xiong, Z.; Zhao, D.; Harper, Jr. W.F. Sorption and desorption of perchlorate with various classes of ion exchangers: a comparative study. Ind. Eng. Chem. Res. 2007, 46, 9213-9222.


Page 29 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

522 523


(27) American Public Health Association. Standard Methods for the Examination of Water and Wastewater, 18th ed.; Washington, DC, 1992.

524

(28) SenGupta, A. K.; Greenleaf, J. E. Arsenic in Subsurface Water: Its Chemistry and

525

Removal by Engineered Processes. In Environmental Separation of Heavy Metals: Engineering

526

Processes; SenGupta, A. K., Ed.; CRC Press LLC: Boca Raton, FL, 2002; pp 265-306.

527 528

(29) L. Liberti, D. Petruzzelli, F.G. Helfferich, R. Passino, Chloride/sulfate ion exchange kinetics at high solution concentration. Reactive Polym. 1987, 5, 37–47.

529

(30) Sarkar, S.; SenGupta, A.K. A new hybrid ion exchange-nanofiltration (HIX-NF)

530

separation process for energy-efficient desalination: Process concept and laboratory evaluation.

531

J. Mem. Sci. 2008, 324, 76-84.

532

(31) OLI Stream Analyzer, Version 9.0; OLI Systems, Inc.: Cedar Knolls, NJ, 2013.

533

(32) Abdel-Aal, E.A.; Abdel-Ghafar, H.M.; El Anadouli, B.E. New Findings about Nucleation

534

and Crystal Growth of Reverse Osmosis Desalination Scales with and without Inhibitor. Cryst.

535

Growth Des. 2015, 15 (10), 5133-5137.

536 537

(33) Sarkar, S.; SenGupta, A.K. The Donnan Membrane Principle: Opportunities for Sustainable Engineered Processes and Materials. Environ. Sci. Technol. 2010, 44, 1161-1166.

538

(34) Klein, G.; Villena-Blanco, M.; Vermeulen, T. Ion-exchange equilibrium data in the

539

design of a cyclic sea water softening process. Ind. Eng. Chem. Process Des. Dev. 1964, 3 (3),

540

280-287.

541 542 543 544

(35) Hoek, C.V.; Kaakinen, J.W.; Haugseth, L.A. Ion exchange pretreatment using desalting plant concentrate for regeneration. Desalination. 1976, 19 (1-3), 471-479. (36) Kaakinen, J.W.; Eisenhauer, R.J. van Hoek, C. High recovery in the Yuma desalting plant. Desalination. 1977, 23 (1-3), 357-366.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

545

(37) Wilf, M. Konstantin, M. Chencinsky, A. Evaluation of an ion exchange system

546

regenerated with seawater for the increase of product recovery of reverse osmosis brackish water

547

plant. Desalination. 1980, 34 (3), 189-197.

548 549 550 551

(38) Barba, D.; Brandani, V.; Foscolo, P.U. A method based on equilibrium theory for a correct choice of a cationic resin in sea water softening. Desalination. 1983, 48 (2), 133-146. (39) Vermeulen, T. Tleimat, B. W.; Klein, G. Ion-exchange pretreatment for scale prevention in desalting systems. Desalination. 1983, 47 (1-3), 149-159.

552

(40) Muraviev, D.; Khamizov, R.Kh.; Tikhonov, N.A.; Morales, J.G. Clean (“Green”) Ion-

553

Exchange Technologies. 4. High-Ca-Selectivity Ion-Exchange Material for Self-Sustaining

554

Decalcification of Mineralized Waters Process. Ind. Eng. Chem. Res. 2004, 43, 1868-1874.

555

(41) Tokmachev, M.G.; Tikhonov, N.A.; Khamizov, R.Kh. Investigation of cyclic self-

556

sustaining ion exchange process for softening water solutions on the basis of mathematical

557

modeling. React. Funct. Polym. 2008, 68, 1245-1252.

558 559 560 561

(42) Venkatesan, A.; Wankat, P.C. Desalination of the Colorado River water: A hybrid approach. Desalination. 2012, 286, 176-186. (43) Abdulgader, H. Al; Kochkodan, V.; Hilal, N. Hybrid Ion Exchange – Pressure Driven Membrane Processes in Water Treatment: A Review. Sep. Purif. Technol. 2013, 116, 253–264.

562


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