McCabe Thiele plot for copper extraction: Fig. 1. McCabe Thiele plot for copper extraction (Aqueous : Cu =0.920 g/L in sulfate solution, pH = 4.70, Organic : 5% ...
EPD Congress 2010 TMS (The Minerals, Metals & Materials Society), 2010
EXTRACTION OF COPPER FROM SULFATE LEACH SOLUTION CONTAINING MINOR METALLIC CONSTITUENTS IN MIXER SETTLER UNIT Vinay Kumar1, Manis Kumar Jha1, Manoj Kumar2, J. Jeong2 and Jae- chun Lee2 1
Metal Extraction and Forming Division, National Metalllurgical Laboratory (NML), Jamshedpur-831007, India 2 Minerals and Materials Processing Division, Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon- 305-350, Korea Keywords: Solvent extraction, e-Wastes Leach liquor, Copper, Mixer settler unit Abstract The present investigation describes R & D studies carried out for recovery of copper from the sulfate solution expected from the leaching of e-wastes in presence of minor constituents such as cadmium, zinc and nickel using solvent extraction process. In order to extract copper in continuous mode in mixer settler unit (MSU), basic studies have been made to optimize the experimental condition using 5%LIX84 in kerosene. Subsequently, the solvent extraction of copper was made in MSU maintaining leach solution flow rate 4.0 L/h and A/O ratio 1. The results showed complete extraction (~97%) of copper in three stages at A/O ratio 1 from the aqueous solution containing 1.98g/L Cu at pH 1.91 in presence of impurities. Loaded metal was completely stripped after scrubbing with 10% sulfuric acid in two stages. The stripped solution could be used for metal/ salt recovery by electrolysis/ crystallization. Introduction E-wastes contain various metallic and non-metallic values. Some of the substances present in ewastes are precious and hazardous in nature and their disposal causes not only the loss of resources but also pollutes the environment [1, 2] The recycling of e-wastes becomes valuable due to the presence of precious metals in it and make the process economically viable [3]. However, their recycling is very complicated due to the heterogeneity of the materials present in the product [4]. Usually, the physical beneficiation followed by hydro/pyrometallurgical processes is employed for the recovery of valuable metallic components of e-scraps. The enriched metallic fraction is leached in acidic/ alkaline solution to dissolve the desired components leaving gangue as the residue. The metal is then recovered following precipitation, ion exchange, solvent extraction, electrolysis etc. Recently, a review on current technologies and treatment status in China for recycling of waste printed circuit boards has been reported by Huang et al. [5]. Out of the various hydrometallurgical processes, the solvent extraction is one of the technique employed on commercial scale for extraction and separation of various non-ferrous metals from leach solutions of low grade ores/secondaries such as complex sulphide ores, brass ash, converter slag etc using different organic extractants [6-10]. Several commercial copper solvent extraction-electrowinning (SX-EW) plants use different organic hydroxyoxime based extractants to produce copper [11]. Depending on the metallic constituents present in the solution, specific processing scheme is developed with different extractants from the leach solutions. Attempts are also being made to recover metallic values from various other resources such as leach liquor of electronic scraps etc using SX process. 413
The sulfuric acid is most commonly employed for the leaching of metals on commercial scale and the subsequent recovery following solvent extraction using organic extractants such as LIX 84, LIX622, Cyanex272, DEHPA etc [8, 12-16] due to easy handling and environmental friendly. LIX84 (2-hydroxy-5-t-nonylacetophenoneoxime) is used on commercial scale for production of copper [6]. The modelling of copper extraction from acidic solutions using LIX84 has been reported [17]. Nam et al. [18] developed a process for recovery of copper, nickel, cobalt from the matte of the polymetallic sea nodules following pressure leaching-solvent extraction route. Reddy and Priya [19] developed a process for extraction and separation of Cu(II), Ni(II) and Zn(II) using LIX84I as an extractant from sulfate solution. At NML, various processes were developed for extraction of metals following solvent extraction route [20]. The studies have been also made for separation of copper and zinc from the leach solution obtained in the treatment of a complex sulfide concentrate [21, 22] using LIX64N at NML. Copper was selectively extracted from the leach liquor leaving zinc in the raffinate. The loaded copper was stripped with strong sulfuric acid and metal produced by electrowinning in a closed-loop SX-EW operation. Further studies were made to compare the performance of LIX84 with LIX64N for separation of copper and zinc from sulfate solutions [23] in presence of impurities like Fe and Mn. LIX84 also exhibited better selectivity for extraction of copper in presence of iron and manganese. Experimental Synthetic solution of required concentration of copper, cadmium, zinc and nickel were prepared by dissolving their salts in distilled water. The organic reagent LIX84 procured from the M/s Cognis Corporation, Ireland (Earlier M/s Henkel Inc., Tucson), mixed with appropriate quantities of kerosene as diluent has been used for the solvent extraction (SX) and separation of copper from th solution. LIX84 is water insoluble 2-hydroxy-5-nonylacetophenone oxime mixed with 5-dodecylsalicylaldoxime and kerosene (high flash point oil). The organic and aqueous solution was mixed under different conditions in a vessel for pre-determined time intervals. The organic and the aqueous phases have been allowed to settle as distinct layers in a separating funnel. The continuous extraction and separation of metals has been also studied using mixersettler unit (pump mix type) after establishing the basic parameters on bench scale. The unit used in this study had 620-mL mixer and 860-mL settler volume. The number of stages adjusted in the continuous trial was as follows: four in co-extraction, two in water scrubbing with two in copper stripping. All the SX experiments have been carried out at room temperature. Metal analysis in the aqueous solution was done with an atomic absorption spectrometer. The metal content in the organic phase was ascertained by analyzing the aqueous phase upon stripping with 180g/L sulfuric acid. Extraction of the metal was computed by analyzing the aqueous and organic phases: a satisfactory material balance was observed in all the cases. All the reagents used were of AnalaR/LR grade chemical without any further purification. Results and Discussion Solvent extraction studies have been carried out for the extraction and separation of the copper in presence of other minor impurities such as cadmium, zinc and nickel from the sulfate solution expected from the e-scraps using LIX84 diluted in kerosene. The results of the investigation are described below.
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Extraction of copper: Effect of pH: The effect of pH has been studied for the extraction of copper in the pH range of 0.94 to 2.65 using 0.92 g/L Cu solution in sulfate medium using 5% LIX84 diluted in kerosene. The pH of the solution has been adjusted with the addition of 1N sodium hydroxide solution. The results indicate increase in copper extraction from 59.23% to 98.73% with increase in pH from 0.94 to 2.18 from aqueous feed at A/O ratio 1 maintaining an equilibrium time 5 minutes. Subsequent increase in pH, the extraction of copper increases 99.06 at pH 2.65. Effect of A/O ratio: The effect of A/O ratio on extraction of copper has also been studied from aqueous feed solution containing 0.92 g/L at pH 4.7 using 5% LIX84 diluted in kerosene. The extraction of copper increased from 44.70% to 87.40% with increasing organic concentration (A/O) from 5/1 to 1/1 maintaining a mixing time of 5 minutes. The equilibrium pH of the solution was found to be 1.60 after extraction of copper with 5% LIX84. On increasing the organic concentration to A/O to 1/3, the extraction of copper marginally increased to only 91.03% due to decrease in equilibrium pH to 1.65. For complete extraction of metal, the adjustment of pH is required. McCabe Thiele plot for copper extraction: 2.5
2
[Cu]org
1.5
1
3rd 0.5
2nd 1st
0 0
0.5
1
1.5
2
[Cu]aq.
Fig. 1. McCabe Thiele plot for copper extraction (Aqueous : Cu =0.920 g/L in sulfate solution, pH = 4.70, Organic : 5% LIX84 in kerosene )
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In order to determine the stage requirement for copper extraction in continuous mode in mixer settler unit (MSU), the 5% LIX84 diluted in kerosene was contacted several time with aqueous feed containing 0.92 g/L at pH 4.7 and A/O ratio 1. McCabe Thiele diagram was plotted as metal in organic phase against metal in aqueous phase in equilibrium. The isotherm given in Figure-1 indicates three stage requirements for complete extraction of copper at A/O ratio 1. Accordingly, the number of stages has been fixed in mixer settler unit for metal recovery.
Extraction and separation of copper in Mixer Settler Unit: After establishing the condition for the extraction of copper in separating funnel, the studies have been carried out in mixer-settler unit (MSU). Effect of pH during extraction of copper in MSU: After adjusting the flow rate of all the aqueous and organic phases, the SX studies were carried out using model leach liquor having ~1.98 g/L Cu and minor impurities like 0.1 g/L of Cd, Zn and Ni each. During continuous extraction process, the pH of the solution was found to decrease with extraction of copper in different mixing compartments of the unit due to generation of hydrogen ion according to the reaction mentioned below. CuSO4 + 2RH
