Solid–Liquid Stable Equilibrium of the Aqueous Quaternary System

Article pubs.acs.org/jced

Solid−Liquid Stable Equilibrium of the Aqueous Quaternary System NH4SCN−(NH4)2S2O3−(NH4)2SO4−H2O at 303.15 K Dongchan Li,†,‡ Fei Li,§ Yingying Zhao,†,‡ and Junsheng Yuan*,†,‡ †

School of Marine Science and Engineering, ‡Engineering Research Center of Seawater Utilization Technology, Ministry of Education, §School of Chemical Engineering, Hebei University of Technology, 300130 Tianjin, China ABSTRACT: The salts of thiocyanate, thiosulfate, and sulfate exist in a variety of industrial processes such as textile, coking, and electroplating. The effluents from these industries cannot be discharged directly owing to their severe environmental pollution. In addition, there is an opportunity to recover significant commercial value from these effluents. The phase equilibria and phase diagram play a major role in separating and recovering useful resources. In this paper, the phase diagrams of the system NH4SCN− (NH4)2S2O3−(NH4)2SO4−H2O and its subsystems at 303.15 K were determined by an isothermal dissolution equilibrium method. In the phase diagram of the quaternary system, there is one invariant point, three univariant curves and three crystallized regions. The invariant point is cosaturated with ammonium thiocyanate, ammonium sulfate, and ammonium thiosulfate (NH4SCN + (NH4)2SO4 + (NH4)2S2O3). The three crystallization regions correspond to ammonium sulfate ((NH4)2SO4), ammonium thiocyanate (NH4SCN), and ammonium thiosulfate ((NH4)2S2O3). The first one is the largest area, but the latter two are much smaller ones. The phase diagram can be utilized to separate and recover NH4SCN, (NH4)2SO4, and (NH4)2S2O3 selectively and individually from the desulfurization effluents. The result of this paper shows that the environmental pollutant can be converted to the valuable product by a simple, economical, and green process.

■

INTRODUCTION In recent years, thiocyanate, thiosulfate, and sulfate are widely found in a number of industrial processes such as textile manufacturing, metal separation, coking, photofinishing, electroplating, and so on.1−3 Before being discharged, these industrial wastewaters must be treated and removed because of their severe harm to human and organisms.4−7 They can also cause serious and persistent pollution to the environment, because they are difficult to hydrolyze and they have the nature of low volatility. 8−11 These salts have very important commercial values and are widely used in steel, construction, mining, dyeing, photography, agrochemical, and pharmaceutical industries.12−14 Therefore, separating and recovering of these salts from such industrial effluents become an urgent task for the sake of economic and environmental concerns. It is worth noting that these salts are difficult to be separated from each other because they always coexist in the industrial effluents and have a similar solubility and close molecule sizes. The traditional methods to solve the problem include electrodialysis,15 membrane filtration,16,17 wet-oxidation,18 biological treatment,7 ion exchange,19,20 adsorption,21,22 and so on. However, the above methods suffer from high costs, low yields, complex processes, long times or low efficiency. Moreover some of these methods need large tank capacities, usage of toxic reagents, harsh oxidizing conditions, as well as limitations of effluents, and so on. Therefore, a new cheap and effective method is highly demanded to separate and recover the salts from the industrial effluents. As we know the phase diagrams and phase equilibria play a major role in developing and utilizing resources,23,24 and it has the prior application in many © 2014 American Chemical Society

industries with its cost-effective, energy-saving, and green process. It has further become a promising and potential method for the separating and recycling of such salts from industrial effluents. This study focuses on the salt mixture (NH4 SCN, (NH4)2S2O3, and (NH4)2SO4) in the industrial wastewater during the desulfurization process which mostly uses ammonia as an alkaline source.2,3,17−19 When the total concentration of salt mixture exceeds 250 g·L−1, it will seriously affect the effectiveness of the gas desulfurization.25,26 While discharged directly with the wastewater even though being diluted not only means a severe environmental pollution as waste source, it also causes the loss of significant economic values. Because the mixed salts are rather difficult to separate from each other, the phase diagrams and equilibria of the system NH4SCN− (NH4)2S2O3−(NH4)2SO4−H2O and its subsystems at 303.15 K were developed in this work. So far, no other data on the system NH4SCN−(NH4)2S2O3−(NH4)2SO4−H2O at 303.15 K are available to resolve the problem of treating and reclaiming the corresponding salts from the desulfurization wastewater.

■

EXPERIMENTAL SECTION Apparatus and Reagents. The instruments in this equilibrium study consist of three parts: a thermostat, test Received: August 7, 2014 Accepted: November 20, 2014 Published: December 15, 2014 82

dx.doi.org/10.1021/je500738g | J. Chem. Eng. Data 2015, 60, 82−88

Journal of Chemical & Engineering Data

Article

measured by titration with a standard solution of Na2S2O3 in the procedure of saturated bromine solution, phenol solution, KI, and the indicator is starch (precision: ± 0.50 %),10 or it can be calculated by subtraction via ion balance.

tubes strapped on a disc, and an electric stirrer. The disc with test tubes was fixed on the electric stirrer. When the electric stirrer has been started, the sealed tubes on the disc were rotated with the turning disc simultaneously until the solid− liquid equilibrium has been reached. The whole experiment was carried out in the thermostat, which can automatically control the temperature at (303.15 ± 0.5) K. The solid phase minerals were identified with the wet residue method of Schreinmaker and the X-ray diffractometer (D8 Focus, Bruker AXS, Germany). The densities (ρ) of the equilibrium liquids were measured by a density bottle method with a precision of ± 0.0002 g·cm−3. Chemicals. The chemicals in the experiment include ammonium thiocyanate, ammonium sulfate, ammonium thiosulfate and water. All the chemicals used were of analytical-purity grade, and the amounts of purities were more than 99.0 % (NH4SCN, 99.0 % (w/w), (NH4)2SO4, 99.5 % (w/w), and (NH4)2S2O3, 99.5 % (w/w)). The water was distilled with electrical conductivity less than 1.0 × 10−4 S·m−1 and pH 6.60 in the whole study. Experimental Methods. The solid−liquid stable equilibrium was studied with the isothermal dissolution equilibrium method. First, according to relevant phase equilibrium compositions, 2 5 ,2 6 the appropriate salts (NH 4 SCN, (NH4)2SO4, and (NH4)2S2O3) and distilled water were placed and sealed in the equilibrium tubes, which must ensure the solids were not dissolved entirely and always existed in the whole equilibrium process. Then the sealed tubes were rotated with the turning disc for several hours at a thermostat in which the water submerged the tubes with the temperature at (303.15 ± 0.5) K. The liquid phases were sampled every 2 h and analyzed. If two samples gave the identical analysis results, then the solid−liquid equilibrium reached. The preliminary experiment has confirmed that 24 h is the optimum time which can ensure the equilibrium being reached for the system at 303.15 K. After rotating for 24 h, the tubes were allowed to settle and separate for at least 2 h in the thermostat with the temperature at (303.15 ± 0.5) K. Then the samples of the equilibrium solutions and wet residues were analyzed, respectively. The liquid samples were taken from the solution with the syringes equipped with a filter, which both were previously heated at 303.15 K slightly to prevent precipitation during sampling. Then the liquid samples were weighed and diluted to 250 mL volumetric flask with distilled water for the chemical analysis. The corresponding wet residues of the samples were separated with vacuum filtration and dried at (303.15 ± 0.5) K and then weighed and diluted for the chemical analysis. The solid was determined by the X-ray diffraction method for further identification. Analytical Methods. The compositions of NH4+ in the liquid phases and wet residues were determined by a method of acid−base titration with precision ± 0.30 %. It was titrated by the standard NaOH solution and phenolphthalein as the indicator with the presence of formaldehyde solution neutralized before use.10 The SO42− in the liquid was first reacted with barium chloride to generate the barium sulfate sediment, and then the superfluous barium ions are titrated by standard EDTA solution (deduct the consumption of EDTA for Ca2+, Mg2+) with the existence of Mg-EDTA at pH 10; the indicator is eriochrome black T (precision: ± 0.60 %). The S2O32− concentration was titrated with the standard iodine solution in the presence of acetic acid, and then the indicator is starch (precision: ± 0.30 %).10 The SCN− concentration was

■

RESULTS AND DISCUSSION Ternary System NH4SCN−(NH4)2S2O3−H2O at 303.15 K. The experimental solubility of the ternary system NH4SCN−(NH4)2S2O3−H2O at 303.15 K are determined and presented in Table 1. The solution composition is expressed by mass fraction. The corresponding phase diagram is presented in Figure 1. Table 1. Equilibrium Solubilities of the Ternary System (NH4SCN + (NH4)2S2O3 + H2O) at 303.15 K and Pressure p = 0.1 MPaa composition of liquid phase w(B)·102 no.

(NH4)2S2O3

H2O

NH4SCN

equilibrium solid phase

1 2 3 4 5 6 7 8 9 10 11 12 13 14

0 5.72 12.21 16.11 21.14 23.73 29.02 34.41 37.08 41.27 46.12 52.23 57.22 62.51

32.5 32.12 31.34 30.14 28.9 27.96 26.57 27.68 29.16 31.23 34.02 36.56 37.3 37.49

67.5 62.16 56.45 53.75 49.96 48.31 44.41 37.91 33.76 27.5 19.86 11.21 5.48 0

SN2 SN2 SN2 SN2 SN2 SN2 SN1+SN2 SN1 SN1 SN1 SN1 SN1 SN1 SN1

a

Note: Standard uncertainties u are u(T) = 0.50 K, ur(p) = 0.05; ur(NH4+) = 0.0030, ur(SCN‑) = 0.0050, ur(S2O32‑) = 0.0030; SN1(NH4)2S2O3, SN2- NH4SCN.

Figure 1 shows that there is one invariant point E, two univariant curves DE and FE, and two crystallization regions

Figure 1. Equilibrium phase diagram of the ternary system ((NH4)2S2O3 + NH4SCN + H2O) at 303.15 K. ●, experimental point; , experimental isotherm curve. 83

dx.doi.org/10.1021/je500738g | J. Chem. Eng. Data 2015, 60, 82−88

Journal of Chemical & Engineering Data

Article

DEB and FEC. The invariant point E is cosaturated with ammonium thiocyanate and ammonium thiosulfate (NH4SCN + (NH4)2S2O3). The points D and F are the single-salt solubility of ammonium thiocyanate and ammonium thiosulfate, respectively. The univariant curve DE is saturated with NH4SCN and the univariant curve FE is saturated with (NH4)2S2O3. The two crystallization regions DEB and FEC are corresponding to the NH 4 SCN saturation area and (NH4)2S2O3 saturation area. Neither double salt nor solid solution is formed in the studied system. The invariant point E is confirmed with the Schreinemakers graphic method. Through analyzing the composition of liquid phase in point E and the corresponding wet residue M, the experiments proved the eutectic point E cosaturated with NH4SCN and (NH4)2S2O3, which is the so-called Schreinemakers graphic method.

Table 2. Equilibrium Solubilities of the Ternary System ((NH4)2S2O3 + (NH4)2SO4 + H2O) at 303.15 K and Pressure p = 0.1 MPaa composition of liquid phase w(B)·102 no.

(NH4)2S2O3

H2O

(NH4)2SO4

equilibrium solid phase

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

0 5.55 7.22 12.64 15.99 20.50 25.54 30.27 35.39 40.70 47.92 51.83 55.62 56.72 59.03 60.04 62.51

56.68 55.46 55.1 53.74 52.78 51.67 49.80 48.59 46.19 43.66 40.58 38.81 37.60 36.05 36.79 37.27 37.49

43.32 38.99 37.68 33.62 31.23 27.83 24.66 21.14 18.42 15.64 11.50 9.36 7.88 6.23 4.18 2.69 0

SN3 SN3 SN3 SN3 SN3 SN3 SN3 SN3 SN3 SN3 SN3 SN3 SN3 SN3+SN1 SN1 SN1 SN1

a

Note: Standard uncertainties u are u(T) = 0.50 K, ur(p) = 0.05; ur(NH4+) = 0.0030, ur(S2O32‑) = 0.0030, ur(SO24−) = 0.0060; SN1(NH4)2S2O3, SN3- (NH4)2SO4.

Figure 2. Equilibrium phase diagram of the ternary system ((NH4)2S2O3 + (NH4)2SO4 + H2O) at 303.15 K. ●, experimental point; , experimental isotherm curve.

The diagram of the system NH4SCN−(NH4)2S2O3−H2O at 303.15 K can be utilized to separate NH4SCN and (NH4)2S2O3 selectively from their mixed solution by adding mother liquor or salt, which can make the system point in diagram move to the corresponding crystallization region then achieve the separation purpose. The result enables reclaiming the single salt from the desulfurization wastewater containing NH4SCN and (NH4)2S2O3 and converting them from pollutant to the valuable product. Ternary System (NH4)2SO4−(NH4)2S2O3−H2O at 303.15 K. The experimental solubility of the ternary system (NH4)2SO4−(NH4)2S2O3−H2O at 303.15 K are determined and listed in Table 2. The solution composition is expressed by mass fraction. The corresponding phase diagram is plotted in Figure 3. It shows that there is one invariant point E, two univariant curves DE and FE, and two crystallization regions DEB and FEC. The invariant point E is cosaturated with ammonium sulfate and ammonium thiosulfate ((NH 4 ) 2 SO 4 + (NH4)2S2O3). The points D and F are the single-salt solubility of ammonium sulfate and ammonium thiosulfate, respectively. The univariant curve DE is saturated with (NH4)2SO4 and the univariant curve FE is saturated with (NH4)2S2O3. The two

Figure 3. Equilibrium phase diagram of the ternary system ((NH4)2SO4 + NH4SCN + H2O) at 303.15 K. ●, experimental point; , experimental isotherm curve.

crystallization regions DEB and FEC are corresponding to the large saturation area of (NH4)2SO4 and the relative small saturation area of (NH4)2S2O3. Neither double salt nor solid solution is formed in the studied system. The invariant point E is confirmed with the Schreinemakers graphic method. Analyzing the composition of the liquid phase in point E and the corresponding wet residue M proved the eutectic point E coexisted with (NH4)2SO4 and (NH4)2S2O3, which is the so-called Schreinemakers graphic method. The diagram of the system (NH4)2SO4−(NH4)2S2O3−H2O at 303.15 K can be utilized to separate (NH4)2SO4 and (NH4)2S2O3 selectively from their mixed solution by adding mother liquor or salt, which can make the system point in 84

dx.doi.org/10.1021/je500738g | J. Chem. Eng. Data 2015, 60, 82−88

Journal of Chemical & Engineering Data

Article

curve DE is saturated with (NH4)2SO4 and the univariant curve FE is saturated with NH4SCN. The two crystallization regions DEB and FEC are corresponding to the large saturation area of (NH4)2SO4 and the much smaller saturation area of NH4SCN. Neither double salt nor solid solution is formed in the studied system. The invariant point E is confirmed with the Schreinemakers graphic method. Analyzing the composition of the liquid phase in point E and the corresponding wet residue M proved the eutectic point E coexisted with (NH4)2SO4 and NH4SCN, which is so-called Schreinemakers graphic method. The diagram of the system (NH4)2SO4−NH4SCN−H2O at 303.15 K can be utilized to separate (NH4)2SO4 and NH4SCN selectively from their mixed solution through the way of adding mother liquor or salt, which can make the system point in diagram move to the corresponding crystallization region then to achieve the separation purpose. The result meets the requirements for reclaiming the single salt from the desulfurization wastewater containing (NH 4 ) 2 SO 4 and NH4SCN and converting them to a valuable product. Quaternary System NH4SCN−(NH4)2SO4−(NH4)2S2O3− H2O at 303.15 K. The experimental solubility and the relevant density of the quaternary system NH4SCN−(NH4)2SO4− (NH4)2S2O3−H2O at 303.15 K are determined and listed in Table 4. The solution composition is expressed with weight percentage wb and Jäenecke index Jb (g/100g dry salt) respectively. With the data of the Janeche index Jb in Table 4, the corresponding phase diagram of the quaternary system is plotted in Figure 4. The phase diagram of the quaternary system in Figure 4 consists of one invariant point E, three univariant curves and three crystallized regions. The invariant point E is cosaturated with three salts - ammonium thiocyanate, ammonium sulfate, and ammonium thiosulfate (NH4SCN + (NH4)2SO4 + (NH4)2S2O3). The three univariant curves correspond to E1E, E2E, E3E are saturated with (NH4)2SO4 + (NH4)2S2O3, (NH 4 ) 2 SO 4 + NH 4 SCN, and NH 4 SCN + (NH 4 ) 2 S 2 O 3 separately. The three crystallization regions CE2EE1, BE2EE3, and AE1EE3 correspond to ammonium sulfate ((NH4)2SO4), ammonium thiocyanate (NH4SCN), and ammonium thiosulfate ((NH4)2S2O3). The crystallizatiton region of (NH4)2SO4 is much bigger than the others. The solid phase minerals in invariant point E are identified with the X-ray diffraction method. And the XRD patterns in Figure 5 confirmed the three salts (NH4SCN, (NH4)2SO4, (NH4)2S2O3) coexisted in the wet residue of the invariant point E. Neither double salt nor solid solution is formed in the quaternary system. The water diagram of the quaternary system at 303.15 K is shown in Figure 6. The figure shows that the Jänecke index values of water J(H2O) gradually change with increasing J((NH4)2S2O3) and there is the lowest Jänecke index of water at the invariant point E. According to the density data in Table 4, the relationship diagrams of the solution densities vs the composition of J((NH4)2S2O3) are plotted in Figure 7. It can be found that the densities of the equilibrium solutions gradually increase with the increasing ((NH4) 2S2O3) concentration, and reach maximum values at cosaturation point E in Figure 7. The diagram of the quaternary system NH 4 SCN− NH4)2SO4−(NH4)2S2O3−H2O at 303.15 K can be utilized to separate NH4SCN, (NH4)2SO4, and (NH4)2S2O3 selectively from their mixed solution through the way of adding mother liquor or salt, which can make the system point in diagram

diagram move to the corresponding crystallization region then to achieve the desired separation result. The result meets the requirements for reclaiming the single salt from the desulfurization wastewater containing (NH 4 ) 2 SO 4 and (NH4)2S2O3 and converting a pollutant into a valuable product. Ternary System (NH4)2SO4−NH4SCN−H2O at 303.15 K. The experimental solubility of the ternary system (NH4)2SO4− NH4SCN−H2O at 303.15 K are determined and listed in Table 3. The solution composition is expressed with mass fraction. The corresponding phase diagram is presented in Figure 4. Table 3. Equilibrium Solubilities of the Ternary System ((NH4)2SO4 + NH4SCN + H2O) at 303.15 K and Pressure p = 0.1 MPaa composition of liquid phase w(B)·102 no.

(NH4)2SO4

H2O

NH4SCN

equilibrium solid phase

1 2 3 4 5 6 7 8 9 10 11 12 13 14

0 1.03 2.66 4.20 5.40 7.23 9.32 13.12 16.71 19.38 24.19 28.86 34.94 43.32

32.50 34.55 32.81 34.11 37.31 43.49 46.32 51.40 53.65 55.60 57.11 57.83 57.85 56.68

67.50 64.42 64.53 61.69 57.29 49.28 44.36 35.48 29.64 25.02 18.70 13.31 7.21 0

SN2 SN2 SN2+SN3 SN3 SN3 SN3 SN3 SN3 SN3 SN3 SN3 SN3 SN3 SN3

a

Note: Standard uncertainties u are u(T) = 0.50 K, ur(p) = 0.05; ur(NH4+) = 0.0030, ur(SCN‑) = 0.0050, ur(SO24−) = 0.0060; SN2NH4SCN, SN3- (NH4)2SO4.

Figure 4. Equilibrium phase diagram of the quaternary system (NH4SCN + (NH4)2S2O3 + (NH4)2SO4 + H2O) at 303.15 K. ●, experimental point; , experimental isotherm curve.

It shows that there is one invariant point E, two univariant curves DE and FE, and two crystallization regions DEB and FEC. The invariant point E is cosaturated with ammonium sulfate and ammonium thiocyanate ((NH4)2SO4 + NH4SCN). The points D and F are the single-salt solubility of ammonium sulfate and ammonium thiocyanate, respectively. The univariant 85

dx.doi.org/10.1021/je500738g | J. Chem. Eng. Data 2015, 60, 82−88

Journal of Chemical & Engineering Data

Article

Table 4. Equilibrium Solubilities and Densities of the Quaternary System (NH4SCN + (NH4)2S2O3 + (NH4)2SO4 + H2O) at 303.15 K and Pressure p = 0.1 MPaa composition of liquid phase w(B)·102

composition of liquid phase Jäneck index/(g/100g S)

no.

(NH4)2S2O3

NH4SCN

(NH4)2SO4

H2O

(NH4)2S2O3

NH4SCN

(NH4)2SO4

H2O

density ρ/g·cm−3

equilibrium solid phase

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

56.72 55.76 54.67 50.67 47.82 45.06 41.13 40.56 38.01 37.84 32.56 30.12 29.78 0 2.46 6.16 7.64 12.49 17.19 21.52 26.15 30.63 30.05

0 1.41 3.9 11.16 14.92 18.54 23.04 24.4 27.22 27.74 34.78 38.31 39.8 64.53 62 58.21 56.98 52.64 48.75 44.65 40.33 44.36 42.3

6.23 6.05 5.42 5.13 5.16 5.25 4.87 4.32 3.95 3.9 2.56 2.11 2.77 2.66 2.97 3.44 3.27 3.05 2.98 3.03 3.4 0 0.79

37.05 36.78 36.01 33.04 32.1 31.15 30.96 30.72 30.82 30.52 30.1 29.46 27.65 32.81 32.57 32.19 32.11 31.82 31.08 30.8 30.12 25.01 26.86

90.10 88.20 85.44 75.67 70.43 65.44 59.58 58.54 54.94 54.46 46.58 42.7 41.16 0 3.65 9.08 11.25 18.32 24.94 31.10 37.42 40.85 41.09

0 2.23 6.09 16.67 21.97 26.92 33.37 35.22 39.35 39.93 49.76 54.31 55.01 96.04 91.95 85.85 83.93 77.21 70.74 64.52 57.71 59.15 57.83

9.90 9.57 8.47 7.66 7.60 7.63 7.06 6.24 5.71 5.61 3.66 2.99 3.83 3.96 4.40 5.07 4.82 4.47 4.32 4.38 4.87 0 1.08

58.86 57.58 57.01 49.34 47.28 45.24 44.84 44.34 44.55 43.93 43.06 41.76 38.22 48.83 48.30 47.47 47.30 46.67 45.10 44.51 43.10 33.35 36.72

1.2590

SN1+SN3 SN1+SN3 SN1+SN3 SN1+SN3 SN1+SN3 SN1+SN3 SN1+SN3 SN1+SN3 SN1+SN3 SN1+SN3 SN1+SN3 SN1 +SN3 SN1+SN2+SN3 SN2+SN3 SN2+SN3 SN2+SN3 SN2+SN3 SN2+SN3 SN2+SN3 SN2+SN3 SN2+SN3 SN1+SN2 SN1+SN2

1.2790 1.2827 1.2948 1.3032 1.3038 1.3056 1.3093 1.3163 1.1654 1.1792 1.1903 1.2222 1.2417 1.2558 1.2737 1.2896

a Note: Standard uncertainties u are u(T) = 0.50 K, ur(p) = 0.05, ur(ρ) = 2.0 × 10−4 g·cm−3; ur(NH4+) = 0.0030, ur(S2O32‑) = 0.0030, ur(SCN‑) = 0.0050, ur(SO24−) = 0.0060; SN1- (NH4)2S2O3, SN2- NH4SCN, SN3- (NH4)2SO4.

Figure 5. X-ray diffraction pattern of the invariant point E (NH4SCN + (NH4)2SO4 +(NH4)2S2O3 + H2O) at 303.15 K.

■

CONCLUSION The solid−liquid equilibria of the quaternary system NH4SCN−(NH4)2SO4−(NH4)2S2O3−H2O and its subsystems at 303.15 K were determined by an isothermal dissolution equilibrium method. The various phase diagrams were constructed. In the quaternary system, there is one invariant point, three univariant curves and three crystallized regions.

move to the corresponding crystallization region then to achieve the purpose of separating the salts from each other. The result meets the requirements for reclaiming the single salt from the desulfurization wastewater containing NH 4 SCN, (NH4)2SO4, and (NH4)2S2O3 and converting them from pollutant to a valuable product. 86

dx.doi.org/10.1021/je500738g | J. Chem. Eng. Data 2015, 60, 82−88

Journal of Chemical & Engineering Data

Article

reclaiming the salts of ammonium thiocyanate, ammonium sulfate, and ammonium thiosulfate (NH4SCN, (NH4)2SO4, and (NH4)2S2O3) from their industrial wastewater.

■

AUTHOR INFORMATION

Corresponding Author

*Tel: +86(22)60202241. Tel: +86(22)60204598. E-mail: [email protected]. Funding

The work was financially supported by the National Nature Science Foundation of China (21406048, 21306037, and U1232112), applied basic research plan of Hebei Province (13963103D), Natural Science Foundation of Tianjin (13JCQNJC05600, 14JCYBJC20700), and High Level Talents Project of Hebei Province (C2013003041). Notes

The authors declare no competing financial interest.

■

Figure 6. Water phase diagram of the system (NH4SCN + (NH4)2S2O3 + (NH4)2SO4 + H2O) at 303.15 K.

REFERENCES

(1) Valente, J. S.; Tzompantzi, F.; Prince, J.; Cortez, J. G. H.; Gomez, R. Adsorption and photocatalytic degradation of phenol and 2,4 dichlorophenoxiacetic acid by Mg−Zn−Al layered double hydroxides. Appl. Catal., B 2009, 90, 330−338. (2) Yu, X.; Chang, Z.; Sun, X. M.; Lei, X. D.; Evans, D. G.; Xu, S. L.; Zhang, F. Z. Co-production of high quality NH4SCN and sulfur slow release agent from industrial effluent using calcined MgAl−hydrotalcite. Chem. Eng. J. 2011, 169, 151−156. (3) Wu, T.; Sun, D. J.; Li, Y. J.; Zhang, H.; Lu, F. J. Thiocyanate removal from aqueous solution by a synthetic hydrotalcite sol. J. Colloid Interface Sci. 2011, 355, 198−203. (4) Vicente, J.; Diaz, M. Thiocyanate Wet Oxidation. Environ. Sci. Technol. 2003, 37, 1452−1456. (5) Lai, P.; Zhao, H.; Wang, C.; Ni, J. Advanced treatment of coking wastewater by coagulation and zero-valent iron processes. J. Hazard. Mater. 2007, 147, 232−239. (6) Kononova, O. N.; Kholmogorov, A. G.; Danilenko, N. V.; Goryaeva, N. G.; Shatnykh, K. A.; Kachin, S. V. Recovery of silver from thiosulfate and thiocyanate leach solutions by adsorption on anion exchange resins and activated carbon. Hydrometallurgy 2007, 88, 189− 195. (7) Zhu, X. P.; Ni, J. R.; Lai, P. Advanced treatment of biologically pretreated coking wastewater by electrochemical oxidation using boron-doped diamond electrodes. Water Res. 2009, 43, 4347−4355. (8) Lai, P.; Zhao, H. Z.; Wang, C.; Ni, J. R. Advanced treatment of coking wastewater by coagulation and zero-valent iron processes. J. Hazard. Mater. 2007, 147, 232−239. (9) Jeong, Y. S.; Chung, J. S. Biodegradation of thiocyanate in biofilm reactor using fluidized-carriers. Process Biochem. 2006, 41, 701−707. (10) Chen, R.; Hu, X. E. Electrosorption of thiocyanate anions on active carbon felt electrode in dilute solution. J. Colloid Interface Sci. 2005, 290, 190−195. (11) Li, Y. J.; Gao, B. Y.; Wu, T.; Chen, W. S.; Li, X.; Wang, B. Adsorption kinetics for removal of thiocyanate from aqueous solution by calcined hydrotalcite. Colloids Surf., A 2008, 325, 38−43. (12) Yang, K. S.; Theil, M. H.; Chen, Y. S.; Cuculo, J. A. Formation and characterization of the fibres and films from mesophase solutions of cellulose in ammonia/ammonium thiocyanate solvent. Polymer 1992, 33, 170−174. (13) Sharghi, H.; Nasseri, M. A.; Nejad, A. H. Efficient synthesis of βhydroxy thiocyanates from epoxides and ammonium thiocyanates using tetraarylporphyrins as new catalysts. J. Mol. Catal. A 2003, 206, 53−57. (14) Kumbasar, R. A. Separation and concentration of cobalt from zinc plant acidic thiocyanate leach solutions containing cobalt and nickel by an emulsion liquid membrane using triisooctylamine as carrier. J. Membr. Sci. 2009, 333, 118−124. (15) Oda, T.; Matsubara, A. Japanese Pat. (1981) JP80-34943.

Figure 7. Density vs composition in the quaternary system (NH4SCN + (NH4)2S2O3 + (NH4)2SO4 + H2O) at 303.15 K. ▲, experimental value; , experimental relationship diagram.

The invariant point is cosaturated with ammonium thiocyanate, ammonium sulfate and ammonium thiosulfate (NH4SCN + (NH4)2SO4 + (NH4)2S2O3). The three crystallization regions are corresponding to ammonium sulfate ((NH4)2SO4) which is the largest area, ammonium thiocyanate (NH4SCN), and ammonium thiosulfate ((NH4)2S2O3) which are much smaller ones. This research provides the fundamental data and gives the theoretic guidance for successfully treating the desulfurization wastewater. The diagram of the system NH 4 SCN− (NH4)2SO4−(NH4)2S2O3−H2O at 303.15 K can be utilized to separate NH4SCN, (NH4)2SO4, and (NH4)2S2O3 selectively from their mixed solution through the way of adding mother liquor or salt, which can make the system point in diagram move to the corresponding crystallization region then to separate the salts from each other. The result meets the requirements for separating and reclaiming the single salt from the desulfurization wastewater and converting them from pollutant to a valuable product. This method has several advantages since it is cost-effective, saves energy, uses mild reaction conditions, and overall is a green process. It has the promising and potential application in separating and 87

dx.doi.org/10.1021/je500738g | J. Chem. Eng. Data 2015, 60, 82−88

Journal of Chemical & Engineering Data

Article

(16) Yin, N.; Zhong, Z. X.; Xing, W. H. Ceramic membrane fouling and cleaning in ultrafiltration of desulfurization wastewater. Desalination 2013, 319, 92−98. (17) Yin, N.; Yang, G.; Zhong, Z. X.; Xing, W. H. Separation of ammonium salts from coking wastewater with nanofiltration combined with diafiltration. Desalination 2011, 268, 233−237. (18) Sato, T.; Takeda, K. Japanese Pat. (1982) JP80-91122. (19) Sato, T.; Nakamura, T.; Takeda, K. Japanese Pat. (1982) JP8083805. (20) Dizge, N.; Demirbas, E.; Kobya, M. Removal of thiocyanate from aqueous solutions by ion exchange. J. Hazard. Mater. 2009, 166, 1367−1376. (21) Geng, C. Y.; Xu, T. H.; Li, Y. P.; Chang, Z.; Sun, X. M.; Lei, X. D. Effect of synthesis method on selective adsorption of thiosulfate by calcined MgAl-layered double hydroxides. Chem. Eng. J. 2013, 232, 510−518. (22) Li, Y. J.; Yang, M.; Zhang, X. J.; Wu, T.; Cao, N.; Wei, N.; Bi, Y. J.; Wang, J. Adsorption removal of thiocyanate from aqueous solution by calcined hydrotalcite. J. Environ. Sci. 2006, 18, 23−28. (23) Deng, T. L.; Li, D. C. Solid−liquid metastable equilibria in the quaternary system (NaCl−KCl−CaCl2−H2O) at 288.15 K. Fluid Phase Equilib. 2008, 269, 98−103. (24) Yuan, J. S.; Li, F.; Zhao, Y. Y.; Guo, X. F.; Li, S. Y.; Li, D. C. Liquid−Solid Equilibrium of the KCl−NH4Cl−NH3−H2O System with Different NH3 Contents at (273.15 and 298.15) K. J. Chem. Eng. Data 2013, 58, 1391−1397. (25) Cao, J. Y.; Kong, X. B. Recovery of ammonium salts from desulfurization waste water with ternary phase diagram theory. Fuel Chem. Processes 2000, 31, 265. (26) Yuan, G. M.; Tang, G. R. Recovery of ammonium thiocyanate by ternary phase diagram theory from coking waste water. Appl. Chem. Ind. 2008, 37, 1070−1073.

88

dx.doi.org/10.1021/je500738g | J. Chem. Eng. Data 2015, 60, 82−88