Environmental-Friendly Process for Recovering Copper and Nickel

Jun 11, 2014 - Engineering and Technology Research Center for Inorgnic Type Ion-Exchange Resin, Henan University, Kaifeng, Henan 475004, P.R. China...
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Environmental-Friendly Process for Recovering Copper and Nickel from Jinchuan Tailings by Silica-Based Selective Adsorbents Xin Li,*,†,‡ Baohua Li,§ Jiajia Deng,§ Tingting Lu,§ Shan Wang,§ Jingbing Li,§ Dongsheng Chen,*,‡,§ Yuqiang Liu,∥ and Shaohua Wang∥ †

School of the Chemistry and Environment, Jiaying University, Meizhou, Guangdong 514015, P.R. China Engineering and Technology Research Center for Inorgnic Type Ion-Exchange Resin, Henan University, Kaifeng, Henan 475004, P.R. China § Luoyang Dingli Environmental Protection Technology Co., Limited, Luoyang, Henan 471012, P.R. China ∥ Jinchuan Group Limited, Jinchang, Gansu 737100, P.R. China ‡

ABSTRACT: Contamination of heavy metals from mill tailings is a global problem. China’s Jinchuan Group Limited has stored approximately one billion tons of mill tailings which contain toxic levels of copper, nickel, and other metal compounds. To solve the problem, this work extended the principle of hydrometallurgical extraction to the recovery of copper/nickel from Jinchuan tailings and designed an environmental-friendly recovering process. Synergetic leaching by sulfuric acid and ferric ion was proposed to achieve the efficient leach of copper, nickel, and other metals in Jinchuan tailings. Novel silica-based 2aminomethylpyridine and iminodiacetic acid functionalized adsorbent were used to selectively recover copper and nickel from the leachate of Jinchuan tailings, respectively. The stable adsorption capacity on semi-industrial scale operation after 700 continuous adsorption-regeneration runs promises the achievement of copper and nickel recovery from Jinchuan tailings. the ion exchange13,14 technique are two major methods for the recovery of copper/nickel. Substantial tests proved that organic extractants and solvents used in the solvent extraction process are typically toxic and flammable and tend to cause environmental pollution problems. The other alternative is the use of the polymer-based ion-exchange resin as an extraction medium. Unfortunately, the most widely used polymer-based resin for copper/nickel extraction, i.e., iminodiacetic acid functionalized cross-linked polystyrene, is easily fouled by ferric ions and loses the ability to extract copper and nickel. For this reason, iminodiacetic acid functionalized cross-linked polystyrene is not suitable to extract Cu(II)/Ni(II) ions from the iron-rich leachate of Jinchuan tailings. Recently, we fabricated a series of silica-based functionalized adsorbents in an attempt to overcome these problems.15−17 The rigid nature of the silica matrix allows the adsorbents to keep superior stability and durability in frequent adsorptionregeneration cycles; meanwhile, the hydrophilic nature of the silica matrix enables the adsorbents to have more rapid adsorption kinetics than polymer-based ion-exchange resin. Of these silica-based adsorbents, two are most promising for copper/nickel recovery. One is 2-aminomethylpyridine functionalized adsorbent (abbreviated as SB-AMPy adsorbent) which can selectively extract Cu(II) ions in the perturbation of Fe(III) ions,15 and the other is iminodiacetic acid functionalized adsorbent (abbreviated as SB-IDA adsorbent) which can

1. INTRODUCTION Mining activities have created a global problem in the form of mill tailings that are generated during mineral processing and are usually composed of varied heavy metals. It is estimated that Jinchuan Group Ltd., the China’s leading producer of nickel, cobalt, and platinum group metals and second largest producer of copper, has deposited nearly one billion tons of mill tailings from the flotation of metal sulfide minerals. There are huge amounts of copper, nickel, iron, and other metal minerals in the tailings. An oxidized zone with depleting metal sulfide content, developed during the past decades, has been detected, indicating that the metal sulfides have been increasingly converted to oxidized minerals. The natural in situ oxidation of Jinchuan tailings probably occurred by the catalysis of acidophilic iron(II)- and sulfur-oxidizing bacteria.1−4 It is difficult for the low-grade copper/nickel minerals in the tailings to be upgraded by flotation technology and further refined by pyrometallurgical methods; therefore, the hydrometallurgical process is a natural choice for the recovery of copper/nickel. The hydrometallurgical process generally involves minerals leaching, metal extraction from the leachate, and electrowinning. The typical leaching process for copper/ nickel sulfide minerals includes bioleaching,5,6 sulfuric acid leaching7 and oxidation leaching by ferric ions (i.e., ferric ions are added to oxidize insoluble copper/nickel sulfides into soluble copper(II)/nickel(II) ions and elemental sulfur).8 The naturally occurring iron element in Jinchuan tailings may be used to improve the copper/nickel recovery in the leaching process. However, ferric and other ion assemblages will raise a troublesome question of how to efficiently separate copper/ nickel from the leachate. Generally, solvent extraction9−12 and © 2014 American Chemical Society

Received: Revised: Accepted: Published: 11137

April 13, 2014 June 9, 2014 June 11, 2014 June 11, 2014 dx.doi.org/10.1021/ie501527r | Ind. Eng. Chem. Res. 2014, 53, 11137−11144

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Scheme 1. Reaction Pathway Yielding SB-AMPy and SB-IDA Adsorbents

Table 1. Elemental Contents in Jinchuan Tailings and Dissolved Metal Concentrations in the Resultant Leachate element

Cu

Ni

Co

Fe

Mg

Al

Ca

Mn

O

Si

S

tailings (wt %) leachate (g/L)

0.285 0.683

0.348 0.789

0.027 0.029

9.18 13.40

28.19 38.10

0.453 0.529

0.215 0.280

0.166 0.222

40.50

19.74

0.896

efficiently extract Cu(II) or Ni(II) ions in the presence of Fe(II) ions.16 In this paper, we extended the principle of hydrometallurgical extraction to the recovery of copper/nickel from the Jinchuan tailings. Synergetic leaching by sulfuric acid and ferric ions was proposed to achieve the efficient leach of copper, nickel, and other metals in the Jinchuan tailings. Then, the copper was recovered by SB-AMPy adsorbent and nickel by SB-IDA adsorbent, respectively. Other metals were successively recovered by chemical methods. By organizing these individual processes, an environmental-friendly process was designed for recovering copper, nickel, and other metals from Jinchuan tailings.

chloropropyl trimethoxysilane (CPTMOS) in a toluene bath to produce chloropropylated silica. In this reaction, CPTMOS was hydrolyzed first by the hydrated water molecule monolayer; then, the hydrolyzed products were attached to the silanols on the silica surface through a hydrogen bond, followed by Si−O formation with concomitant loss of water. After removing the unreacted CPTMOS, the chloropropylated silica was reacted with polyallylamine aqueous solution to yield silica-polyallylamine composites (SPC). N-Alkylation between chlorine of 2-chloromethylpyridine and primary amino groups of SPC was then carried out to produce the SB-AMPy adsorbent. Similarly, SB-IDA adsorbent could be obtained by the N-alkylation between chlorine of chloroacetic acid and primary amino groups of SPC. All the synthetic steps for the formation of the SB-AMPy and SB-IDA adsorbents are presented in Scheme 1. A sample of SB-AMPy and SB-IDA adsorbents underwent elemental analysis (EA) on a PerkinElmer 2400 instrument to determine the nitrogen content.

2. MATERIALS AND METHODS 2.1. Tailings Sample Collection and Analysis. Samples were collected from the Jinchuan tailings site at 10 different locations and from a depth of 200 cm. After collection, tailings were sieved through a 100 mesh screen to obtain fine earth fraction and then dried to constant weight at 80 °C in a vacuum dryer. A nondestructive chemical analysis of the tailings sample was performed on an X-ray fluorescence spectrometer (Shimadzu XRF-1800). 2.2. Fabrication of SB-AMPy and SB-IDA Adsorbent. Raw silica with particle size of 150−500 μm was pretreated with an amount of water that leads to approximately one monolayer. The resultant hydrated silica was then treated with γ-

3. RESULTS AND DISCUSSION 3.1. Tailings Analysis and Leach. Jinchuan tailings consist mainly of sulfide, oxide, sulfate, and silicate of varied metals. Elemental contents (including Cu, Ni, Co, Fe, Al, Ca, Mg, Mn, O, Si, and S) of the tailings sample obtained by XRF are listed in Table 1. The low level of sulfur in the tailings suggested that the metal sulfides have been converted to highly oxidized minerals. Clearly, oxide and sulfate of metals could be easily 11138

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Scheme 2. Adsorption Mechanism of SB-AMPy and SB-IDA Adsorbents

Figure 1. Effect of pH on the copper adsorption capacity of SB-AMPy and on the nickel adsorption capacity of SB-IDA adsorbents at 298 K, with an initial copper and nickel concentration of 1000 mg/L, respectively.

of SB-AMPy adsorbent (%): N, 5.08; C, 17.41; H, 3.44; and of SB-IDA adsorbent (%): N, 2.72; C, 13.88; H, 3.29. It is easily calculated that nitrogen contents were 3.63 mmol/g for SBAMPy adsorbent and 1.94 mmol/g for SB-IDA adsorbent, respectively. Because each AMPy group contains 2 nitrogen atoms, the loading capacity of the AMPy group on the exterior and interior surface of SB-AMPy adsorbent is easily calculated to be 1.815 mmol/g. Similarly, a loading capacity of 1.94 mmol/g for IDA group on the SB-AMPy adsorbent is obtained since each nitrogen atom may constitute one IDA functional group. From the loading capacities of functional groups and the chelating mode of the functional group-metal ion, the theoretical adsorption capacity may be estimated. 3.3. Adsorption Performances and Selectivity of SBAMPy and SB-IDA Adsorbents. Figure 1 depicted the effect of pH on copper and nickel adsorption capacity from a batch experiment at 298 K with an initial copper and nickel concentration of 1000 mg/L, respectively. In the pH range of 1.0−5.0, the copper adsorption capacity of SB-AMPy adsorbent increased by raising pH and the maximum capacity of 0.69 mmol/g was observed at pH of 5.0. It was also seen that SBAMPy adsorbent exhibited a high copper adsorption capacity even in a lower pH (0.44 mmol/g at pH 1.0 and 0.55 mmol/g at pH 2.0). When pH exceeds 5.0, copper adsorption capacity will never increase by raising pH, whereas precipitation of Cu(OH)2 may occur according to its solubility product. Thus, a pH below 5.0 is recommended for copper adsorption operation. In the adsorption of SB-IDA adsorbent for Ni(II), an increase in pH resulted in a significant rise in Ni(II) adsorption capacity and the maximum adsorption capacity of 0.45 mmol/g was observed at pH of 5.0. Likewise, a higher pH may result in precipitation of Ni(OH)2. Therefore, a pH of ca. 5.0 is preferred for the nickel adsorption process.

dissolved by sulfuric acid to release corresponding ions. On the other hand, the leached Fe(III) ion will significantly improve the leach of the remaining sulfide minerals by its strong oxidization. Therefore, a synergetic leach process with sulfuric acid-ferric ion was proposed for Jinchuan tailings. Herein, the synergetic leaching process only rests on the naturally leached Fe(III) ion from the tailings without the addition of foreign Fe(III) ion. A pilot test of synergetic leach for Jinchuan tailings was conducted in a series of leaching tanks (each tank with size of 5000 mm inner diameter and 5000 mm length) with overhead stirrer; the H2SO4 solution of 35 wt % was used for the leach with a liquid-to-solid ratio of 2.5−3.0, and the operating temperature was controlled in the range of 20−30 °C. Both recovery of copper and nickel greater than 89% after 3 days suggested an efficient leach for Jinchuan tailings. The contents of major metals in leachate were also given in Table 1. Another advantage of the synergetic leach with sulfuric acidferric ion is that the leach may be achieved in a very low cost because a yearly production of ca. 1,000,000 tons of sulfuric acid was formed in Jinchuan Group Ltd. as a byproduct during the pyrometallurgical manufacture of copper, nickel, and cobalt from sulfide minerals. In China’s undeveloped areas, such as the adjacent regions of Jinchuan Group Ltd. or even the entire northwest of China, the consumption of so much sulfuric acid seems to be difficult, and a great part of it is usually on sale with no profit margin. Therefore, the excess sulfuric acid is directly used for the leach. 3.2. Loading Capacities of the Functional Groups of SB-AMPy and SB-IDA Adsorbents. Elemental analysis was employed to estimate the loading capacities of 2-aminomethylpyridine (AMPy) and iminodiacetic acid (IDA) functional groups on the SB-AMPy and SB-IDA adsorbents, respectively. Following were the results of elemental analysis

Table 2. Copper Adsorption Capacity of SB-AMPy (Determined at pH 2.0) and Nickel Adsorption Capacity of SB-IDA (Determined at pH 5.0) with the Perturbation of Some Metal Ions at 298 K, with an Initial Concentration of 1000 mg/L for Each Ion copper or nickel adsorption capacity with different perturbing ions (mmol/g)

a

adsorbent/ion type

Cu(II)

Ni(II)

Co(II)

Mn(II)

Fe(II)

Ca(II)

Mg(II)

Al(III)

Fe(III)

SB-AMPy/Cu SB-IDA/Ni

0.55 0.25

0.55 0.45

0.55 0.43

0.55 0.44

0.54 0.44

0.55 0.45

0.55 0.45

0.55 0.44

0.55 0.01a

The nickel adsorption capacity of SB-IDA with the perturbation of Fe(III) ion was determined at pH 2.0 to avoid the precipitation of Fe(OH)3. 11139

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Figure 2. Environmental-friendly process for recovering copper, nickel, and other metals from Jinchuan tailings.

Figure 3. Major operations for recovering copper (left) and nickel (right).

Figure 4. Appearance of both adsorbents: a-1 and a-2 are SB-AMPy without and with adsorbed Cu(II); b-1 and b-2 are SB-IDA without and with adsorbed Ni(II).

Adsorption selectivity in the presence of perturbing ions is of great importance for the practical use of SB-AMPy and SB-IDA adsorbents. Table 2 revealed that, under the experimental conditions of 298 K and pH 2.0, the copper adsorption capacity of SB-AMPy adsorbent maintained a value of above 0.55 mmol/g with the perturbation of Fe(III), Fe(II), Ni(II), Co(II), etc. It may be concluded that SB-AMPy adsorbent only adsorbed Cu(II) while rejecting other metal ions. At pH > 2.0, Fe(III) ion tends to precipitate; a pH of no more than 2.0 is therefore recommended for the recovery of copper in the presence of Fe(III) ion.

Figure 5. Semi-industrial scale fixed-bed column experiments for recovering copper (left) and nickel (right).

It is also seen from Table 2 that, in the perturbation of Cu(II) and Fe(III), the nickel adsorption capacity of SB-IDA adsorbent significantly decreased from 0.45 mmol/g to 0.25 and 0.01 mmol/g, respectively. The adsorption capacity 11140

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Figure 6. Adsorption breakthrough curves of Cu(II), Ni(II), Co(II), Fe(III), and Mg(II) ions in Cu(II) recovery column experiments.

Figure 7. Adsorption breakthrough curves of Ni(II), Co(II), Fe(II), and Mg(II) ions in Ni(II) recovery column experiments.

underwent a negligible drop in the presence of other perturbing ions, maintaining a stable value of at least 0.43 mmol/g, however. Adsorption preferences of SB-IDA adsorbent were obtained in the sequence Fe(III) ≫ Cu(II) > Ni(II) ≫ Co(II) > Al(III) > Mn(II) > Fe(II) > Ca(II) > Mg(II). Such adsorption preferences are very consistent with the sequence of the formation constants of EDTA-metal ions complexes. The strong selective adsorption of SB-AMPy adsorbent toward Cu(II) ion can be explained as follows. In the ligand of 2-aminomethylpyridine, the secondary amine group and pyridine are classified as borderline bases, which require a borderline acid to form a strong interaction according to hard− soft acid−base (HSAB) theory.18,19 Of all the metal ions in the Jinchuan leachate, Fe(III), Al(III), Mn(II), Ca(II), and Mg(II) ions are hard acids and not likely to form a stable complex with 2-aminomethylpyridine. The remaining Cu(II), Ni(II), Co(II), and Fe(II) ions are borderline acids and seem to coordinate with 2-aminomethylpyridine. It is known that Ni(II), Co(II), and Fe(II) tend to form a hexacoordinated complex. Owing to the steric hindrance of the polyallylamine chain, it is difficult for 2-aminomethylpyridine to form a hexacoordinated complex

with Ni(II), Co(II), or Fe(II) ions. This hindrance may be ignored in the tetrahedral grouping of the ligand with a tetracoordinated ion such as Cu(II), however. In this situation, two 2-aminomethylpyridine ligands coordinate with one Cu(II) ion by the formation of two five-membered chelate rings, as shown in Scheme 2. Clearly, the structure of 2-aminomethylpyridine and the particular steric factor ensure the copper selectivity of SB-AMPy adsorbent. In the case of SB-IDA adsorbent, the functional group, iminodiacetic acid, is essentially a half ethylenediaminetetraacetic acid (EDTA) molecule. The metal ions are likely bonded in a tridentate fashion through the amine and both carboxylic acid groups of the functional group, and eventually, each metal ion can form a six-coordinated complex with two iminodiacetic acid ligands. The stability of the complex is achieved by the formation of four five-membered chelate rings, as shown in Scheme 2. During the loading stage, a number of metal ions may coload onto SB-IDA adsorbent and some metal ions may be displaced by those with stronger binding affinities. For example, copper will displace nickel and nickel will displace cobalt. Eventually, Fe(III) ions will displace all the other metal

Table 3. Concentration Comparisons of Major Metal Ions in Feed, Effluent, Rinse, and Strip Solution During an AdsorptionRegeneration Run of Cu(II) and Ni(II) Recovery Column Experimentsa solution type feed 1 effluent effluent rinse 1 strip 1 feed 2 effluent effluent rinse 2 strip 2

1Bc 1Ac

2Bc 2Ac

concentration of metal ions (g/L) volume (L)

Cu(II)

Ni(II)

Co(II)

Mg(II)

ironb

3700 3400 300 500 59 2800 2300 500 500 50

0.683 0.0004 0.260 0.345 38.55 0.0004 0 0 0.0003 0.0193

0.789 0.770 0.770 0.138 0.0172 0.770 0.0005 0.368 0.504 34.35

0.029 0.027 0.027 0.014 0.0006 0.027 0.021 0.021 0.025 0.085

38.10 37.86 37.86 1.776 0.0012 37.86 36.48 36.48 7.694 0.228

13.40 12.59 12.59 5.912 0.5232 12.59 11.68 11.68 4.995 0.145

a Material balance equations of each metal ion are given for copper recovery VF1CF1 = VE1BCE1B + VE1ACE1A + VR1CR1 + VS1CS1 and for nickel recovery VF2CF2 = VE2BCE2B + VE2ACE2A + VR2CR2 + VS2CS2, where VF, VE, VR, and VS represent the volume of feed, effluent, rinse, and strip solution, respectively; CF, CE, CR, and CS are the concentration of each ion in the solution of feed, effluent, rinse, and strip solution, respectively. bIron is presented as Fe(III) in the copper recovery system and Fe(II) in the nickel recovery system. cEffluents 1B and 1A denoted as effluent 1 before and after breakthrough occurred, respectively, and the same with Effluents 2B and 2A. For a single column operation in the copper recovery system, the volumes of breakthrough and saturated adsorption are 34 and 37 BV, respectively. While in the nickel recovery system, the data are 23 and 28 BV, respectively.

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Until saturated adsorption of column A1, the fluids access to this column are closed off and the exhausted SB-AMPy adsorbents in column A1 are ready for regeneration. For the next adsorption-regeneration cycle, the adsorption operation starts from column A2 and then takes place in the connected column A3; i.e., feed solution 1 will be directed upflow to the column A2 and then column A3. During the adsorption, column A1 is being regenerated to be used for the next adsorption-regeneration cycle. The regeneration system includes an acid tank, a clean water tank, a mixing tank, and acid pumps. The exhausted SB-AMPy adsorbents were regenerated by first rinsing with a H2SO4 solution of pH 2.0 for a chase of the residual background ions, followed by the stripping step of the bound Cu(II) ions with H2SO4 solution of 150 g/L, and then washing the adsorbents to pH 2.0 with water for reuse. The chase stream and the acidic regenerant stream are prepared by mixing water and concentrated sulfuric acid within the mixing tank. After Cu(II) ions are removed by the copper recovery system, the effluent 1 is subsequently introduced into the nickel recovery system. Major operations associated with nickel recovery are very similar to those of the copper recovery system. Before nickel adsorption, Fe(III) ions in effluent 1 should be reduced by sodium sulfite to Fe(II) ions and then the pH should be adjusted to 5.0 for optimum adsorption. Upon completion of the nickel adsorption, the exhausted SB-IDA adsorbents were regenerated by a chase with H2SO4 solution of pH 5.0, followed by the strip of Ni(II) ions with a H2SO4 solution of 150 g/L, and then a washing step to pH 5.0 with water for reuse. It is seen from Figure 4 that original SB-AMPy and SB-IDA adsorbents are opaque amber and beige particles, respectively. The SB-AMPy with adsorbed Cu(II) and SB-IDA with adsorbed Ni(II) appear to be dark green and light blue, respectively. The color change is favorable for the judgment of the adsorption process. The semi-industrial scale fixed-bed column experiments were performed on a poly(methyl methacrylate) column (300 mm inner diameter and 1500 mm length) with a bed volume (BV) of 100 L, as shown in Figure 5. In column adsorption operation, a faster flow rate will speed up the velocity of treatment. However, in a fast flow rate, the adsorbents have to be subjected to a high hydrodynamic pressure. When the hydrodynamic pressure exceeds the ultimate strength of the porous adsorbents, it will cause fracture and breakage of the adsorbent particles. Therefore, the flow rate selected would be the result of an appropriate compromise between treatment velocity and hydrodynamics. Herein, a flow rate of 6 BV/h is recommended for column operation. 3.6. Separation and Recovery of Copper/Nickel. After pH adjusting and precision filtration, the leachate was fed into the copper recovery column at a flow rate of 6 BV/h. Figure 6 showed that Cu(II) ions could be efficiently extracted within about 34 BV before a significant breakthrough occurred. The concentration of Fe(III), Mg(II), Ni(II), and Co(II) ions reach a high level even in the early effluent, indicating a poor adsorption of these ions on SB-AMPy adsorbent. The breakthrough curves of Al(III), Ca(II), and Mn(II) ions are not presented in Figure 6 because these ions can hardly be adsorbed by SB-AMPy adsorbent and their relatively low concentrations. It is seen from Table 3 that Cu(II) ions reached a very high concentration in strip solution 1 (38.55 g/L) from a low level

ions; this is why the iminodiacetic acid functionalized resin is easily fouled by Fe(III) ions. 3.4. Total Process for Recovering Metals from Jinchuan Tailings. For the leachate of Jinchuan tailings, Cu(II) ion always precedes to be recovered by SB-AMPy adsorbent regardless of the concentration of Fe(III) and other metal ions. After removal of Cu(II), only Fe(III) has precedence over Ni(II) to be adsorbed by SB-IDA adsorbent. It has been proved that SB-IDA adsorbent will prefer to adsorb Ni(II) while virtually rejecting Fe(II). In this case, if Fe(III) was reduced to be Fe(II), then Ni(II) ion will be easily recovered by SB-IDA adsorbent. Therefore, copper and nickel in Jinchuan tailings may be recovered as follows: SB-AMPy adsorbent is employed to recover Cu(II) from Fe(III) and other ion assemblages at a pH of no more than 2.0. Then, Fe(III) should be reduced to Fe(II) by sodium sulfite (another byproduct of Jinchuan Group Ltd.); after all copper has been removed and Fe(III) has been reduced to Fe(II), SB-IDA adsorbent is used at the optimum pH of 5.0 to recover Ni(II). On the basis of the above optimized conditions, an environmental-friendly process in semi-industrial scale for recovering metals from Jinchuan tailings was designed. The whole process shown in Figure 2 contains four parts: (A) leach of Jinchuan tailing and treatment of leached residues, (B) copper recovery by SB-AMPy adsorbent, (C) nickel recovery by SB-IDA adsorbent, and (D) recovery of iron, manganese, and other metals. The leached residues, mainly including calcium, magnesium, aluminum, and iron in silicate forms, as well as other insoluble compounds, were separated by a filter press. These residues are not ecotoxic and usually returned to the tailings sites. After removal of Cu(II) and Ni(II), the other metal ions remaining in the leachate may be recovered by chemical methods. 3.5. Fixed-Bed Column Equipment and Operation. The semi-industrial scale fixed-bed column operation system for copper and nickel recovery was illustrated in Figure 3. A set of three columns for copper recovery (A1, A2, and A3, packed with SB-AMPy adsorbents) was followed by another set of three columns for nickel recovery (B1, B2, and B3, packed with SB-IDA adsorbents). For each three-column equipment, two of the columns are connected in series, and the third column serves as a spare. The adsorption takes place in the two connected columns while the other one is being purged/ regenerated or otherwise being repaired or undergoing routine maintenance. All treatment streams are introduced in an upflow mode (i.e., the solution was continuously pumped in from the bottom of one column and discharged after treatment from the top of the same column) so that the streams can be in adequate and close contact with the adsorbents. In a practical use, there are breakthrough adsorption and saturated adsorption for a single column operation. Take column A1 as an example, provided a breakthrough concentration is set at the value of 1.0 mg/L (the value should meet the China’s industrial effluent regulation), we may define that breakthrough occurred when the copper in effluent from column A1 exceeds 1.0 mg/L. Generally, the SB-AMPy adsorbents in column A1 have not reached the saturated adsorption when breakthrough occurred. In this case, the copper in effluent from column A1 will be adsorbed by column A2, which ensures that the SB-AMPy adsorbents in column A1 reach the state of saturated adsorption and the copper in the final effluent will never exceed the breakthrough concentration. 11142

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Notes

in feed solution 1 (0.683 g/L); meanwhile, the concentration of Fe(III) ions dropped from 13.40 to 0.5232 g/L, and the coexisting Ni(II), Co(II), and Mg(II) ions also decreased to a very low level. Rinse solution 1 containing substantial Cu(II) ions is directed back to feed solution 1 so as to have all Cu(II) ions recovered. Effluent 1A continues to the next copper adsorption run. Effluent 1B is subsequently introduced into the nickel recovery system after the reduction of Fe(III) into Fe(II) and pH adjusting to 5.0. In Figure 7, a breakthrough volume of ca. 23 BV was observed for Ni(II) onto SB-IDA adsorbent (nickel breakthrough concentration was also set as 1.0 mg/L). Table 3 revealed that Ni(II) ions were concentrated to a high level of 34.35 g/L in strip solution 2 from 0.770 g/L in feed solution 2, while Fe(II) and other metal ions decreased to a very low concentration. Effluent 2B contains a negligible level of Cu(II) and Ni(II) ions, and the level is not toxic according to WHO regulations. Thus, the final treatment for effluent 2B is to recover iron, magnesium, and other metal ions by chemical methods. Effluent 2A continues to the next nickel adsorption run; rinse solution 2 is directed back to feed solution 2 so as to have all Ni(II) ions recovered. To obtain high-quality crystalline copper, the cupric electrolyte used for the electrowinning process should contain >35 g/L of Cu(II) and 60 g/L of Ni(II),