Recovery of high value copper and zinc oxide powder ...

HYDROM-04170; No of Pages 9 Hydrometallurgy xxx (2015) xxx–xxx

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Recovery of high value copper and zinc oxide powder from waste brass pickle liquor by solvent extraction Manish Kumar Sinha a,b, Sushanta Kumar Sahu a,⁎, Swati Pramanik a, Lal Bahadur Prasad b, Banshi Dhar Pandey a a b

Metal Extraction and Forming Division, CSIR-National Metallurgical Laboratory, Jamshedpur 831007, India Department of Chemistry, Banaras Hindu University, Varanasi 221005, India

a r t i c l e

i n f o

Article history: Received 23 May 2015 Received in revised form 14 August 2015 Accepted 15 September 2015 Available online xxxx Keywords: LIX 984N Brass pickle solution Counter-current extraction Hydrothermal synthesis Cu powder ZnO powder

a b s t r a c t Solvent extraction of Cu and Zn from spent brass pickle liquor has been carried out using LIX 984N as an extractant. Very high difference in ΔpH1/2 value for the two metals during the extraction indicates the ease of separating them under the appropriate conditions. Based on the bench scale results, metals were separated in a continuous mode using a laboratory scale mixer settler unit from the spent brass pickling solution containing 35 kg/m3 Cu, 30 kg/m3 Zn, 1.5 kg/m3 Fe, 0.75 kg/m3 Cr, 0.03 kg/m3 Ni and 70 kg/m3 H2SO4 with 30% LIX 984N in kerosene. High copper extraction (99.9%) at the phase ratio (O/A) of 2/1 was obtained at the equilibrium pH of 2.5 in a two-stage counter-current extraction process, leaving behind Zn, Cr and Ni in the raffinate. Zinc from the chromium free solution was then quantitatively extracted in three counter-current extraction stages at pH 5.5 and O/A = 2/1 with negligible co-extraction of nickel. From the respective loaded organic phases, copper and zinc were completely stripped off using 150 kg/m3 H2SO4. The stripped solutions of Cu and Zn were utilized for the synthesis of high pure Cu metal powder and ZnO particles by the hydrothermal reduction/precipitation processes. Copper powder was synthesised in an autoclave at 20 bar H2 pressure and 423 K in 2 h. On the other hand ZnO powder (4 bar) was prepared from zinc striped solution at pH 12 in an autoclave under autogenous pressure at 423 K in 2 h. The purity and morphology of the as-prepared powders were determined by chemical analysis, XRD and SEM-EDS studies. © 2015 Elsevier B.V. All rights reserved.

1. Introduction Industrial wastes generated in metallic industries are generally laden with heavy metals. Brass pickle liquor is also a kind of industrial waste generated during cleaning of the brass surface which tends to build up a black coating by prolonged exposure to the air. The cleaning process involves removal of the oxide layer by dipping the material in dilute sulphuric acid bath, which is usually reused quite a few times before its disposal as a waste. As a result the solution is loaded up with pollutant material such as chromium and high concentration of copper and zinc. Due to its environmentally hazardous and acidic nature it cannot be disposed off without pretreatment. The general treatment of this kind of liquid effluent includes the neutralization by lime. However, this process requires a large amount of alkali/lime resulting in the loss of metal values as well. For the disposal of such industrial wastes, alternate options are increasingly being applied which involves the recovery of the heavy metals as value added products by hydrometallurgical methods in recent years. Recovery of heavy metals as valuable products not only reduces the toxicity of the waste to be disposed off but also conserves natural resources in terms of resource recovery ⁎ Corresponding author. E-mail address: [email protected] (S.K. Sahu).

from the waste streams (Silva et al., 2005). Thus the processing of brass pickle liquor by hydrometallurgical route will definitely provide economic benefits in terms of recovery of value added products of copper and zinc and mitigate the pollution problem arsing due to conventional disposal of waste brass pickle liquor. A number of studies have been reported on the recovery of heavy metals from various waste/secondary resources such as pickle liquors, spent electrolytes, industrial effluents, and brass ash leach liquor. (Sinha et al., 2014; Meshram et al., 2013; Nathsarma, 2002). In all these studies solvent extraction plays a major role in producing high pure precursor solution which is used for making high value products of the heavy metals viz., metal powders, metal oxide powders or salts. Recovery of base metals from copper smelter slag by oxidizing leaching and solvent extraction has been reported by Banza et al. (2002). In this study copper from the leach solution was recovered by solvent extraction with LIX 984 whereas, cobalt and zinc were recovered by solvent extraction with D2EHPA. From the separated solutions metals by electrowinning or metal salts by evaporation-crystallization could be prepared. Sahu et al. (2008) have reported the separation of hexavalent chromium and zinc from electroplating effluent by solvent extraction with tri-n-butyl phosphate and selective stripping with dil. sulphuric acid and sodium hydroxide solutions, respectively. Agrawal et al. (2008) have developed a SX-EW (Solvent extraction-Electrowinning)

http://dx.doi.org/10.1016/j.hydromet.2015.09.012 0304-386X/© 2015 Elsevier B.V. All rights reserved.

Please cite this article as: Sinha, M.K., et al., Recovery of high value copper and zinc oxide powder from waste brass pickle liquor by solvent extraction, Hydrometallurgy (2015), http://dx.doi.org/10.1016/j.hydromet.2015.09.012

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M.K. Sinha et al. / Hydrometallurgy xxx (2015) xxx–xxx

process to recover high value copper and nickel powder from the copper bleed solution. Recently, Meshram et al. (2013) have extensively reported the solvothermal synthesis of high value copper powder from copper bleed solution of an Indian copper smelter using Versatic 10 acid as an extractant. Oxime extractants of LIX series are considered to be among the best reagents for the extraction of base metals because of their performance such as excellent phase separation, low entrainment loss

to the raffinate, rapid metal transfer kinetics and high extractive strength. Besides, they do not promote excessive crud formation. The LIX reagents have therefore, been extensively applied for copper extraction in the moderately acidic conditions (Lazarova and Lazarova, 2005). Out of several variants of LIX reagents, LIX 984 (Miguel et al., 1997; Kongolo et al., 2003; Zhuo-yue et al., 2005; Jian-she et al., 2002; Dara and Benamor, 2002), LIX 984N (Lazarova and Lazarova, 2005; Sridhar et al., 2009; Sridhar and Verma, 2011a, 2011b) and LIX

Table 1 Comparative study of present study with the previously reported data on the solvent extraction of Cu–Zn using LIX 984N. Sources

Synthetic nitrate solution

Composition (kg/m3)

5.0 Cu

Synthetic sulphate bioleaching 10.0 Cu and 20.4 Fe solution

Sulphate leachate of zinc slag

7.66 Cu, 92.75 Zn and 54.42 Cd

Synthetic sulphate solution

2.5 Cu in presence of Zn, Fe and Mn

Synthetic ammoniacal/ammonium carbonate medium

3.0 each of Cu and Ni with 60 kg/m3 ammonium carbonate

Synthetic sulphate solution

0.2 Cu

Synthetic Sulphate solution

0.15 Cu, 0.14 Ni, 0.16 Zn

Polymetallic sea nodules digested in 50% H2SO4

0.360 Cu, 0.365 Ni and 0.040 Co

Nitrate leach solutions of waste PCBs

42.11 Cu, 2.12 Fe, 4.02 Pb, 1.58 Zn and 0.4 Ni

Synthetic sulphate solution (composition similar to the plating wastewater)

1.27 Cu and 1.17 Ni

Sulphate leach liquors

25–27 Cu, ~30 Fe(T), 1.4–1.9 Zn, 0.06–0.1 Co and 0.02–0.03 Ni

Synthetic chloride solution

75.6 Cu, 9.78 Fe, 1.95 Zn, 0.918 Pb, 0.906 Ni, 1.02 Cd, 0.101 Cr, 0.173 Hg, 0.046 Ag, 0.052 As and 0.061 Sb

Waste Brass pickle liquor

35 Cu, 30 Zn, 1.5 Fe, 0.75 Cr, 0.03 Ni and 70 H2SO4

Key Findings Basic study for the SX of Cu at pH 2.0 using different LIX based reagents (5% (v/v)); Extraction trend: LIX 65N b LIX 84N b LIX 984N b LIX 860N-I. Negative ΔGo with LIX 984N indicates the extraction of Cu from nitrate media at low pH values. Achieved high separation factor (βCu/Fe) with 10% LIX 984N at pH 1.5, O/A 1; 98.5% Cu extracted along with b20% Fe; Cu stripping: 97.8% along with 30% Fe with 1.5 kg/m3 H2SO4 at O/A = 1:2. Selective extraction (extraction yield: 87.3%) of Cu with 25% (v/v) LIX 984N at O/A = 3:2, pH 1.7. Zn and Cd separation feasibility tested by D2EHPA, D2EHPA-TBP and HEHEP at pH 2.0 Separation factor calculated at total metal concentration of 2.5 kg/m3 using 18% (v/v) LIX 984N at O/A = 1, pH 2. Extraction order: Cu(II) N Fe(III) N Mn(II) N Fe(II) N Zn(II) at pH 2. Highest separation factor: βCu/Mn = 37, βCu/Zn = 149, βCu/Fe(III) = 17.70, βCu/Fe(II) = 396 at 1.0 kg/m3 Cu and 1.5 kg/m3 of each metal ions. Cu and Ni co-extracted using 20% (v/v) LIX 984N in 2-stages at A/O = 1.9:1, pH 9.2; After ammonia scrubbing at pH 7, Ni selectively stripped using 9.8 g/L H2SO4 in 3-stages at A/O = 1; Cu stripping with 180 kg/m3 H2SO4 in 2-stages at A/O = 1 Examined the synergistic extraction of Cu with Cyanex 301 and LIX 984N. Maximum synergism obtained at 1:1 ratio of Cyanex 301:LIX 984N. Distribution coefficients increased with the initial Cu concentration and temperature. Complete Cu extraction in 2-stages at pH 0.24; 90.65% Cu stripped with 6 M HCl and then it decreases because of formation of easily extractable chlorocomplex. Cu, Ni and Zn extracted at different pH values using LIX 984N = 0.05 M; Cu: 2-stages at A/O = 5.5:1, pH = 3.5; Ni: 2-stages at A/O = 4:1, pH = 7.3; Zn: 2-stages at A/O = 2:1, pH = 8.8; quantitative stripping of Cu and Ni with 2 M H2SO4 and Zn with 3 M H2SO4 Acid neutralized by alkali, Fe precipitated at pH 4.5 and Co(II) converted to Co(III). Cu & Ni co-extracted with 10% LIX 984N leaving Co(III) in the raffinate at A/O = 1 in 8-contacts. After ammonia scrubbing at pH 4, Ni and Cu selectively stripped using 10 kg/m3 and 180 kg/m3 H2SO4 in 2-contacts. Experiment also performed with ACORGA M5640. 99.7% Cu extracted with 1–4 ppm of Zn, Fe, Pb in 3-stages at O/A = 1.5:1, pH 1.5 using 50% (v/v) LIX 984N; Cu stripping: N97% in 4-stages at O/A = 2:1 with spent electrolyte containing 320 kg/m3 H2SO4 and 30.01 kg/m3 Cu. With 15% (v/v) LIX 984N, 92.9% Cu extracted at pH 4 & O/A = 1:1; 93% Ni extracted with 15% (v/v) LIX 984N at pH 10.5 & O/A = 1:1; Cu stripping: N99.1% with 170 kg/m3 H2SO4 at O/A = 1:2; Ni stripping: 99.3% with 200 kg/m3 H2SO4 at O/A = 1:2 Tested extraction behaviour for Cu with LIX 984N, LIX 612N-LV and Acorga M5640. Acid neutralized by alkali. Only 86% Cu extracted in 2-stages at O/A = 4:1, pH 2.2. Fe co-extracted with Cu in LIX 984N. Extraction trend [with 30% (v/v) solvent]: Acorga M5640 N LIX 612N-LV N LIX 984N. Fe extraction increased with decreasing Cu extraction. Cu/Fe ratio in the organic solution increased with increasing Cu extraction as Fe extraction decreased. Order of loading capacity of Cu: LIX 984 N LIX612N-LV, XI04003 N LIX84-I [extractants = 40% (v/v)]; optimum conditions for Cu extraction with low Fe co-extraction: A/O = 2:1, pH b 0.5, T = 40 °C. Acid and Fe removed by SX and precipitation, respectively before extraction of Cu and Zn. Bench scale results applied in lab scale mixer settler unit. Cu selectively extracted at pH 2.5 in 2-stages at O/A 2/1. After Cr precipitation Zn quantitatively extracted at pH 5.5 in 2-stages at O/A 2/1. Stripped solutions used for hydrothermal synthesis of Cu powder and ZnO particles.

References

Lazarova and Lazarova, 2005

Quing-ming et al., 2008

Xie et al., 2008

Asghari et al., 2009

Sridhar et al., 2009

Fouad, 2009

Sridhar and Verma, 2011a

Sridhar and Verma, 2011b

Le et al., 2011

Liqing et al., 2011

Ochromowicz and Chmielewski, 2013

Lu and Dreisinger, 2013

Present study



984N-C (Panda et al., 2012; Kul and Çetinkaya, 2009) have been found to be the quite effective for copper extraction. Use of a synergistic mixture of LIX 984N with Cyanex 301 for copper extraction has also been investigated (Fouad, 2009). In fact, the selective extraction of copper over other heavy metal ions (Ni, Fe and Zn) from various media including acidic waste/leach solutions using LIX 984N, has been reported by several researchers as summarised in Table 1. Quing-ming et al. (2008) reported the extraction of copper from synthetic solution similar to the bioleach liquor of a copper mine (10 kg/m3 Cu and 20.4 kg/m3 Fe, pH 2) using 10% LIX 984N and efficient stripping of loaded organic using 1.5 M H2SO4. Similarly, separation of Cu and Zn from the sulphate leach liquor of a zinc slag (Xie et al., 2008) and from a synthetic solution with LIX 984N (Asghari et al., 2009) was also elaborated. Le et al. (2011) reported the recovery of copper with 50% LIX 984N from the leach solutions of waste PCBs containing 42.11 kg/m3 Cu along with other metals at initial pH 1.5 in nitrate medium. Separation of Cu and Ni from sulphate medium with LIX 984N was examined (Liqing et al., 2011) with the aim of processing the plating wastewater; the optimum pH values for Cu and Ni extraction were found to be 4 and 10.5, respectively. Selective extraction of Ni over Zn and Cd from the sulphate leach solution of cold purification filtration cake of zinc hydrometallurgical plant using 10% LIX 984N at pH 5.3 and O/A ratio of 2, was studied by Balesini et al. (2013). The extraction efficiency of LIX 984N for copper with respect to other chelating extractants was also reported (Ochromowicz and Chmielewski, 2013; Lu and Dreisinger, 2013). Nano-materials/powders have gained considerable attention due to their unique properties and wide application area. Among various nanoparticles, metallic Cu powder and ZnO nanoparticles are extensively popular, which may be due to their excellent optical, electrical and thermal properties, catalytic activities as well as cost effectiveness. Various chemical, physical, and electrochemical methods such as, hydrothermal/solvothermal synthesis, sol–gel, microwave/ultrasoundassisted synthesis, thermal decomposition, electrodeposition, and chemical vapour deposition process, have been applied for the synthesis of Cu/ZnO nanomaterials (Benhebal et al., 2013; Hu et al., 2004; Peulon and Lincot, 1996; Wei et al., 2009; Ni et al., 2005; Shah and Al-Ghamdi, 2011; Meshram et al., 2013). Among the reported methods, hydrothermal process has been considered as a simple way to synthesize the nano-powders because of the involvement of easy and low-cost procedures, moderate temperature, great control over experimental parameters and convenience for the synthesis on large scale (Sinha et al., 2015; Natrchalayuth et al., 2012; Pandey et al., 2000; Agrawal et al., 2006a). It is observed from the literature survey (Table 1) that the previous investigations were mainly based on the basic study for determining the optimum parameters particularly for the extraction of copper with LIX 984N. Although, a few reports are available on the extraction and separation of Cu with other metal ions from original leach solutions, but these are restricted to study the copper purification steps only. Therefore, the present investigation is aimed at developing a complete process for the extraction and separation of copper and zinc from brass pickle liquor using LIX 984N, and synthesis of high value products such as copper powder and zinc oxide particles utilizing the purified solution by hydrothermal precipitation route. The prepared copper and zinc oxide particles were characterized by chemical analysis, SEM and XRD-EDS studies. A process flow-sheet for the recovery of metal values from the spent brass pickle liquor is also given.

3

was recovered by solvent extraction with tris-2-ethylhexyl amine (TEHA) and there after iron was removed by precipitation at pH 3.5. During the acid recovery and iron precipitation loss of copper and zinc due to co-extraction and adsorption on the surface of the precipitated iron hydroxide was almost negligible. Acid and iron depleted waste pickle liquor containing 35 kg/m3 Cu(II), 30 kg/m3 Zn(II), 0.75 kg/m3 Cr(III) and 0.03 kg/m3 Ni(II) was then treated for the extractive separation of copper and zinc using LIX 984N (1:1 mixture of 5-nonyl salicylaldoxime and 2-hydroxy-5-nonylacetophenone oxime) as extractants in kerosene. However, in order to optimize the extraction conditions a synthetic sulphate solution containing 35 kg/m3 Cu or 30 kg/m3 Zn was prepared by dissolving their respective sulphate salts (CuSO4·5H2O and ZnSO4·7H2O). The extractant LIX 984N was supplied by Cognis, Germany and used for the extraction studies without further purification. All other chemicals used in this study were analytical grade reagents. Solvent extraction experiments were carried out by equilibrating equal volumes (except for the construction of McCabe–Thiele diagram) of aqueous solution and the extractant, LIX 984N of known concentration in a stoppered vial using rotospin shaker at 50 rpm. The shaking time of 15 min was found to be sufficient to reach equilibrium. The pH of the aqueous solution was adjusted to the desired value by adding dilute H2SO4 or NaOH solutions. After phase disengagement aqueous and organic phases were separated. Metal ions concentration in the aqueous phase was analysed by Atomic Absorption Spectrometer (Model: ElementAs AAS4141). Metal content in the organic phase was determined by mass balance. Stripping studies of metal ions from the loaded organic was carried out with the dilute sulphuric acid of a known concentration. The high purity copper powder was prepared by the hydrogen reduction of stripped copper solution in an autoclave (titanium vessel-1 L capacity). The copper solution (500 mL) of known composition was heated to the desired temperature, and then hydrogen gas was introduced at a predetermined pressure which was maintained throughout the gaseous reduction. At the end of reduction process, the autoclave was cooled to room temperature. The copper powder produced was filtered over a Buchner funnel using Whatman paper (no. 41), washed with distilled water and rinsed with sodium potassium tartrate solution (2 wt.%) to inhibit the surface oxidation because the synthesized copper powder is susceptible to oxidation (Bagchi et al., 2012). The copper powder thus obtained was dried in an oven at 80 °C overnight. Further, the dried powder was annealed in

2. Materials and method Spent brass pickle liquor containing 35 kg/m3 Cu, 30 kg/m3 Zn, 70 kg/m3 H2SO4, 1.5 kg/m3 Fe (Total), 0.75 kg/m3 Cr and 0.03 kg/m3 Ni was collected from a local brass industry (Jharkhand, India) to recover value added products of copper and zinc from it. Prior to the recovery of copper and zinc, sulphuric acid from the pickle liquor

Fig. 1. Effect of pH on the solvent extraction of copper and zinc. Aq. phase: 35 kg/m3 Cu, 30 kg/m3 Zn, Org. phase: 1 M LIX 984N in kerosene, Phase ratio: 1:1.


4


Fig. 2. Stripping of metal ions from the loaded solvents in single contact. LIX 984N: 34.95 kg/m3 Cu, 29.70 kg/m3 Zn, H2SO4: Different Concentration, Phase ratio: 1:1.

an electrically operated tubular furnace with a flow of hydrogen gas at the desired temperature for proper granulometry, long term storage and prevention of oxidation (Bagchi et al., 2012). In order to prepare the high purity zinc oxide powder, pH of the stripped solution containing zinc was increased by adding 1 M NaOH solution dropwise (3 mL/min) with a constant stirring. When the desired pH (~12) was reached, the solution (500 mL) was autoclaved under the nitrogen atmosphere for 2 h at a pre-set temperature and pressure. The precipitate of ZnO so obtained was cooled and filtered, washed with distilled water and acetone (~50 ml in each experiment); and dried in an oven at 80 °C overnight. The as-prepared copper metal powder and zinc oxide particles were characterized by chemical analysis, XRD and SEM-EDS studies. The XRD data were recorded (Bruker D8-discover) using CuKα radiation in the 2θ range of 10–90o. The powder sample was put on a grid and was coated with gold before recording the SEM (Nova Nano SEM 430).

Fig. 3. Effect of O/A ratio on the extraction of copper and zinc. Aq. phase: 35 kg/m3 Cu and 30 kg/m3 Zn, Org. phase: 1 M LIX 984N in kerosene. Eq. pH = 2.5 for Cu and Eq. pH = 5.5 for Zn.

Fig. 4. McCabe–Thiele Plot for the extraction of copper with LIX 984N. Aq. phase: 35 kg/m3 Cu and 30 kg/m3 Zn, Org. phase: 1 M LIX 984N in kerosene, Eq. pH = 2.5.

3. Results and discussion 3.1. Removal of acid and iron from the pickle liquor In order to remove/recover acid from the pickle liquor the model solution containing 35 kg/m3 Cu, 30 kg/m3 Zn , 70 kg/m3 H2SO4, 1.5 kg/m3 Fe (Total), 0.75 kg/m3 Cr and 0.03 kg/m3 Ni was equilibrated with 40% (v/v) TEHA in kerosene at phase ratio of 2:1. It was observed that almost total acid was extracted into the organic phase in a single contact. It was also noticed that no copper and zinc was co-extracted into the organic phase which may be due to the less affinity of TEHA towards copper and zinc as sulphate. The loaded TEHA was regenerated by stripping with distilled water at 50 °C at a phase ratio (O/A) of unity. It was found that complete H2SO4 were stripped from the loaded TEHA in 2 contacts. Iron from the acid depleted brass pickle liquor was removed by precipitation at pH N3.5. During the precipitation of iron, co-precipitation of copper and zinc was not observed.

Fig. 5. McCabe–Thiele Plot for the extraction of zinc with LIX 984N. Aq. phase: 30 kg/m3 Zn, Org. phase: 1 M LIX 984N in kerosene, Eq. pH = 5.5.



5

3.3. Extraction isotherm and McCabe–Thiele diagram

Fig. 6. Counter-current simulation for the extraction of copper with LIX 984N. Aq. phase: 35 kg/m3 Cu and other metal ions, Org. phase: 1 M LIX 984N in kerosene, O/A = 2:1, Eq. pH = 2.5.

3.2. Solvent extraction of copper and zinc with LIX 984N Acid and iron depleted brass pickle liquor contained 35 kg/m3 Cu(II), 30 kg/m3 Zn(II), 0.75 kg/m3 Cr and 0.03 kg/m3 Ni. In order to establish the separation of copper and zinc from the above solution, a synthetic solution of similar composition (35 kg/m3 Cu(II) and 30 kg/m3 Zn(II)) was used to extract Cu/Zn by equilibrating the solution at the desired pH with 30% LIX 984N (~1 M) in kerosene as the diluent at the phase ratio (O/A) of 1:1 and 30 °C for 15 min. Extraction of copper increased from 10 to 99% in the equilibrium pH range 1.5 to 3.9 without any co-extraction of zinc. Extraction of zinc started at equilibrium pH above 4.5 and increased from 5 to 95% in the equilibrium pH range 4.8 to 6.4 (Fig. 1). The respective pH1/2 values (pH1/2 = the pH corresponding to the extraction of 50% of the metal ions into the organic phase) for Cu and Zn were found to be 2.5 and 5.5. Thus it is clear that 1 M LIX 984N is adequate for selective extraction of copper over zinc with a ΔpH1/2(Zn–Cu) of 3.0, and there is no chance of mutual contamination of one metal with the other during their solvent extraction with LIX 984N. The saturation loading capacity of LIX 984N for Cu (at equilibrium pH 2.5) and Zn (at equilibrium pH 5.5) was also determined separately by repetitive contact of the same organic phase with the fresh aqueous solution at phase ratio 1 until the metal concentration in the raffinate was the same as that of the aqueous feed. The loading capacity of LIX 984N was found to be 34.95 kg/m3 for Cu and 29.70 kg/m3 for Zn after four stages. Stripping of copper/zinc was carried out using meal saturated/ loaded LIX 984N containing 34.95 kg/m3 Cu or 29.70 kg/m3 Zn with different concentrations of sulphuric acid (0.25–1.5 M) at O/A phase ratio of 1. Stripping of both the metal ions increased with an increase in the sulphuric acid concentration (Fig. 2) and with 1.5 M sulphuric acid both the metal ions were stripped quantitatively in a single stage.

The extraction isotherm for copper was obtained by contacting a mixed solution containing 35 kg/m3 Cu and 30 kg/m3 Zn with 1 M LIX 984N in kerosene at different O/A phase ratios (O/A = 1:5 to 5:1) and the equilibrium pH of 2.5. Extraction of copper increased from 18 to 99.9% with the increase in phase ratio. At the entire phase ratio co-extraction of zinc with copper was not observed. The raffinate after complete extraction of copper was used to obtain extraction isotherm for zinc by contacting with 1 M LIX 984N at different phase ratios (O/A = 1:5 to 5:1) and equilibrium pH of 5.5. In the above range of phase ratios zinc extraction increased from 18 to 92.5% (Fig. 3). Using the extraction data obtained from the phase ratio variation, McCabe–Thiele diagram was drawn to determine the number of theoretical counter-current stages required for complete extraction of copper and zinc. It was found from this diagram that two countercurrent extraction stages were sufficient for complete extraction of copper with 1 M LIX 984N at a phase ratio of 2:1 and equilibrium pH 2.5 (Fig. 4). On the other hand three counter-current stages were required for the complete extraction of zinc with 1 M LIX 984N at the phase ratio of 2:1 and equilibrium pH of 5.5 (Fig. 5). Simulation of counter-current extraction of copper or zinc with 1 M LIX 984N (Figs. 6 and 7) showed that at the end of the second stage 17.5 kg/m3 copper and at the end of third stage 14.99 kg/m3 zinc were loaded into the organic phase. The above optimized conditions were applied to separate copper and zinc from the spent brass pickle liquor [35 kg/m3 Cu, 30 kg/m3 Zn, 0.75 kg/m3 Cr and 0.03 kg/m3 Ni] in a laboratory scale mixer settler unit using 1 M LIX 984N in kerosene as the extractant. Before proceeding for mixer settler operation, sulphuric acid and iron were removed from the pickle solution as described in Section 3.1. The resulting Fe(OH)3 precipitate can be stored and processed for the production of pigment. The flow rates of aqueous and organic phase were maintained according to the requirements of the phase ratio (O/A), which was 2:1 as mentioned above. The pH of the solution in every extraction step was maintained to the desired level using required amount of dilute NaOH solution. In the case of extraction of Cu(II) the organic and aqueous flow rates were maintained at 8.12 L/h and 4.05 L/h, respectively at equilibrium pH of 2.5. At the end of the second stage 17.5 kg/m3 Cu was loaded into the organic phase with no contamination of Zn, Cr and Ni. Before zinc extraction chromium from the copper free raffinate was completely removed by precipitation at pH 5.3 using 10% ammonia solution in the presence of ammonium chloride at room temperature (Mahmoud and Barakat, 2001); negligible loss of Zn and Ni was observed in to the precipitate. The resulting hydroxide precipitate of chromium can be used as colouring agent/pigment or as catalyst for organic reactions. After chromium removal the solution [30 kg/m3 Zn(II) and 0.03 kg/m3 Ni] was subjected to solvent extraction of zinc in the mixer settler unit at the equilibrium pH 5.5 and O/A ratio of 2:1 (flow rates of organic = 8.12 L/h and aqueous = 4.05 L/h). After three stages of counter-current extraction 14.99 kg/m3 zinc was loaded in to the organic phase leaving nickel in the raffinate.

Fig. 7. Counter-current simulation for the extraction of zinc with LIX 984N. Aq. phase: 30 kg/m3 Zn and 0.03 kg/m3 Ni, Org. phase: 1 M LIX 984N in kerosene, O/A = 2:1, Eq. pH = 5.5.


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Fig. 10. XRD of ZnO powder produced.

Fig. 8. XRD of copper powder produced by pressure hydrogen stripping.

The high loading of copper and zinc in the two streams of the extractants, is beneficial for the synthesis of the value added products from the respective stripped solutions of high metal concentration. The results show that copper and zinc were completely stripped with 150 kg/m3 sulphuric acid solutions from their respective loaded organic phases at O/A ratio of 1:1 in a single stage. 3.4. Synthesis of the value added products 3.4.1. Hydrothermal synthesis of copper powder The purified copper and zinc solutions generated in the processing of spent brass pickle liquor by solvent extraction with LIX 984N as discussed above, were used for the synthesis of high purity copper metal powder and zinc oxide particles. Copper powder was produced by the reduction of Cu2+ ions present in the purified copper sulphate solution under hydrogen atmosphere in an autoclave at 20 bar H2 pressure, 423 K and 400 rpm for 2 h. The hydrothermal reduction of copper at high temperature and hydrogen pressure from highly acidic copper bleed solution generated from electrolytic unit of copper smelter has been successfully explored and described previously in detail by our research group at CSIR-NML (Agrawal et al., 2006b). From the pressure

and temperature optimization experiments it was concluded that the high temperature and hydrogen pressure were preferred and necessary to enhance reduction kinetics. In the beginning, 1 g copper powder was also added as a seed to accelerate the reaction rate and to avoid copper plating on the stirrer and interior of the reaction vessel (Meshram et al., 2013). Copper seed acts as heterogeneous nucleating site for the nucleation of copper, which have comparatively low energy requirement than that of homogeneous nucleation. This enhances the overall reaction rate and prevents copper plating on the vessel. After the experiment the aqueous filtrate was analysed for copper which was found to be 0.08 kg/m3; the filtrate can be recycled back to the copper stripping circuit. Under the above conditions the recovery of copper as powder was found to be 99.5%. The copper powder obtained was filtered, washed and dried as mentioned earlier before it was annealed at 500 °C in a tubular furnace with a flow of hydrogen gas (5 L/min). The overall reduction of copper sulphate solution to copper powder can be represented as (Agrawal et al., 2006a): Cu2þ þH2 →CuHþ þHþ

ð1Þ

CuHþ þCu2þ →2Cuþ þHþ

ð2Þ

Fig. 9. SEM and EDS of copper powder after annealing.



Fig. 11. SEM and EDS of as-prepared ZnO powder.

Fig. 12. Flow sheet for the recovery of metal values from the brass pickle liquor.


7

8


Cuþ þH2 →CuH þ Hþ

ð3Þ

CuH þ Cuþ →2Cu þ Hþ

ð4Þ

The annealed copper powder was characterized by SEM and XRD. The XRD pattern (Fig. 8) of the copper particles shows the presence of only copper phase as all the peaks agreed well with the reported data for pure copper (JCPDS file No. 04–0836). The sharp diffraction peaks imply that the copper powder has good crystallinity. The purity of the synthesized Cu powder (chemical analysis) was found to be 99.9% with impurity content of 0.015% Zn, 0.018% Fe and 0.005% Ni. The SEM image (Fig. 9a) of the synthesized copper powder after annealing shows that the particle size ranges between 50 and 100 μm with globular shape. High purity of the as-synthesized copper powder is also confirmed by the EDS (Fig. 9b). The copper powder has characteristics suitable for the powder metallurgical (P/M) applications. 3.4.2. Hydrothermal synthesis of ZnO powder from the stripped solution In order to synthesize the ZnO powder, the pH of the purified solution containing 14.99 kg/m3 Zn was raised to 12 by slow addition of 1 M NaOH with constant stirring. The highly basic pH was chosen to ensure product purity and faster growth rate of the zinc oxide particles (Ikono et al., 2012; Baruah and Dutta, 2009; Wu et al., 2011; Wahab et al., 2009a, 2009b; Lu and Yeh, 2000).The precursor solution was then autoclaved at 423 K with stirring at 400 rpm for 2 h under the autogenous pressure (4 bar). The particles obtained was filtered, washed with distilled water and dried overnight in an electrical oven at 80 °C. The hydrothermal conversion of zinc sulphate solution to ZnO can be expressed as (Aimable et al., 2010): Zn2þ þ4OH‐ →ZnðOHÞ4 2‐

ð5Þ

ZnðOHÞ4 2‐ →ZnO þ 2OH‐ þH2 O

ð6Þ

The following conclusions have been drawn: • LIX 984N was found to be selective for copper extraction at lower pH (ΔpH1/2 = 3.0) whereas zinc extraction achieved at higher pH. • The number of counter-current stages for extraction of copper and zinc was determined from the McCabe–Thiele plots. Copper was completely extracted in two counter-current stages in a laboratory scale mixer settler unit using 1 M LIX 984N at equilibrium pH 2.5 and phase ratio (O/A) 2/1. • Zinc was extracted from the copper free raffinate followed by chromium removal, in three counter-current stages using 1 M LIX 984N at the equilibrium pH 5.5 and phase ratio (O/A) 2/1. • From the respective metal loaded organics, copper and zinc were stripped with 150 kg/m3 H2 SO 4 solutions. The globular shaped (50–100 μm size) copper powder of high purity (99.9%) was synthesized from the purified copper solution in an autoclave by hydrogen reduction at 20 bar pressure (H2), 423 K and 400 rpm. • High pure zinc oxide particles of rice grain shape (0.5–1 μm size) were synthesized by hydrothermal precipitation at 423 K and pH 12. The synthesized copper metal powder and zinc oxide particles were characterized by chemical analysis, XRD and SEM-EDS studies, and can be used for various applications.

Acknowledgements Authors are thankful to the Director of the CSIR-National Metallurgical Laboratory (NML), Jamshedpur, India for giving permission to publish the paper. Thanks are also due to DST, Govt. of India for sponsoring the project under RFBR (Russia)-DST (India) bilateral programme (Grant no. INT/ RFBR/P-29/2008). References

At the highly basic conditions, Zn(OH) 24 − species is formed (Aimable et al., 2010; Ma et al., 2005) in the solution and under hydrothermal condition it will dissolve to form Zn2 + and OH− ions. When the ionic product of Zn2 + and OH− exceeds a critical value under supersaturation condition, ZnO nuclei precipitate from the solution and crystal growth begins. The ZnO powder produced was then characterized by SEM and XRD. The sharp X-ray diffraction peaks of hydrothermally prepared powder confirmed that the synthesized ZnO-material was pure and had good crystallinity. All diffraction peaks in the XRD pattern of as-prepared zinc oxide agreed well with the reported data (JCPDS file No. 05–0664) for pure ZnO of hexagonal wurtzite structure (Fig. 10). The purity of the as-produced ZnO powder was found to be N99% as determined by chemical analysis with a yield of ~ 80% Zn. SEM image (Fig. 11a) of ZnO shows that particle size of agglomerated zinc oxide particles ranges between 0.5 and 1 μm with a rice grain shape. The SEM-EDS analysis (Fig. 11b) clearly shows that the sample prepared by the above route has pure ZnO phase. The waste solution after recovering ZnO needs to be further treated to precipitate residual zinc before it is discharged or recycled. 4. Conclusions A complete process has been developed to separate and recover copper and zinc from the spent brass pickle liquor by solvent extraction followed by hydrothermal reduction/precipitation route to produce value added products. A process flow-sheet has been worked out to recover metal values (Fig. 12). Copper and zinc from the spent brass pickle liquor containing 35 kg/m3 Cu, 30 kg/m3 Zn, 0.75 kg/m3 Cr and 0.03 kg/m3 Ni were separated by using LIX 984N. Based on the bench scale results, experiments were also performed in laboratory scale mixer settler unit.

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