Title of Invention

"AN IMPROVED PROCESS FOR THE RECOVERY OF COPPER FORM COPPER PLANT DUST"

Abstract

An improved process for recovery of copper from copper plant dust which comprises, i) grinding the copper dust to about -140 µm in size, ii) characterised in that roasting the above ground copper plant dust at a temperature ranging between 600-800°C for a period of 1 to 4 hours, iii) leaching the above roasted ground copper plant dust in sulphuric acid medium with a solid to liquid ratio in the range of 1: 2.5 to 1: 20 at a temperature ranging from 30°C to 80°C, iv) filtering the above said leached slurry and v) recovering copper from the said filtrate by known method.

Full Text

The present invention relates to an improved process for the recovery of copper from copper plant dust. This invention will be useful for copper industry. During pyrometallurgical processing of copper concentrate, considerable amount of copper loss occurs in the form of dust. It has been found that for processing of 1000 tonnes of concentrate 70-100 tonnes of dust is formed. It contains 25-30% of copper. Also such dust is a serious problem in terms of pollution and storage because of its high content of metal in the form of water soluble compounds and its low apparent density. Therefore, it is necessary to develop a suitable metallurgical processing route to recover copper from copper plant dust. The dust sample are collected from various section of the plant by different collection systems like beneath flues, expansion chambers, baloon flues, boiler settling, filtration through cloth bags in a bag house, electrostatic precipitator in cortell treaters. So far its treatment is concerned, it depend upon the composition of the dust. Usually the dust is charged back to the smelting circuit. In this process the total production capacity of the plant reduces. Various processing routes have been developed. These include (1) Hydrometallurgical processes (2) pyro-hydrometallurgical processes and (3) Pyrometallurgical processes. Several investigators have studied hydrometallurgical processes for recovery of copper from copper dust. Reference may be made to K. Jia Jun , Q. R. Yun and C. Chia Yung, Hydrometallurgy, 14, 1984, pp 217-224, wherein it is described that copper dust is leached with sulphuric acid under atmospheric and high pressure to recover metallic values. However, the process suffers from various drawbacks like large in process inventories, considerable amount of As enters into the leach liquor and copper recovery is poor which reports to the residue as copper sulphide. The residue has to be again fed to copper smelter to recover copper. By this way plant capacity reduces. Reference may be made to C. Nunez, F. Espiell and A. Roca, Hydrometallurgy, 14, 1985, pp. 93-105 wherein it has been described that copper dust is leached with HC1 - NaCl medium, cyclone separation of matte particles and precipitation of iron, arsenic, antimony and bismuth in the presence of calcium ions at a pH of 3.5, leaving the residue of these metal together with lead. The solution from this operation is treated with zinc to cement copper and silver for recycling to the converter. This process suffers from various drawbacks like 50% of copper is recovered, use of costly reagents which can not be recovered from the leach solution. This may affect the economics of the process. Further, use of hydrochloric acid which is corrosive in nature, impose the restriction on materials of construction and create pollution problem with acid fumes. Reference may be made to J. D. Prater and J. S. Wells, US Patent 4149880, Mv 19, 1978, wherein it has been described that smelter flue dust is leached with 40gm/L sulphuric acid at 140°C temperature and under a pressure of 50 psi for solubilising copper values and rendering insoluble the highly toxic values. Copper values were recovered from the solution by cementation on metallic iron. This process also suffers from drawbacks like high investment cost of autoclave besides the skilled persons required to operate autoclave at high temperature and pressure. Reference may be made to W.H. Kruesi and P. R. Kruesi, US Patent 5332560, March 5, 1993, wherein it has been described that copper containing material scrap, ore, dust is leached with cupric tetramine sulphate lixiviant and copper can be recovered from the leachate by electrolysis. This process suffers from drawbacks like use of costly reagent like cupric tetramine sulphate. Reference may be made to K. S. Gritton, D. K. Steele and J. E. Gebhardt Proc. Int. Symp. Recycling of Metals and Engineerd materials Virginia, USA, Oct. 28-31, 1990, wherein it has been described that copper processing flue dusts is leached with sulphuric acid and refinery bleed solution to solubilize As and Cu. As was recovered from leach liquor as As2O3 by reduction and precipitation using SO2. This process suffers from drawback like extra step is required to eliminate As from the leach liquor. Reference may be made to R. Hanks, J. Van der Zel, P. chesney and G. B. Harris, Inst. Min. Met., June 1979, pp C99-C106, wherein it has been described that copper reverberatory dusts is leached with sulphuric acid at 80°C and at a pH value of 1.4, a copper extraction of 83% was obtained with an acid consumption of 3kg acid /kg of Cu. The leach solution contained iron and bismuth level too high for direct electrowinning. Copper was precipitated by adding lime to the leached liquor. This process suffers from drawback like the leach solution contains considerable amount of FeandBi. Reference may be made to W. E. Anable, J. I. Paige and D.C. Paulson, US Bureau of Mines Report Rep. Invest No. 8554, pp 19, 1981, wherein it has been described that cyclone and precipitator dust of copper smelter is treated pyrometallurgically using 110% stoichiometric sulfur and 123% C based on producing a 40% Cu-Fe matte, resulting in recovery of 95% copper contained in the dust. This process suffers from various drawbacks like use of costly sulfur, high temperature operation and pollution. Reference may be made to J. Newton and C. L. Wilson, "Metallurgy of copper", J. Wiley & Sons. Inc., London, pp. 244, 1942, wherein it has been described that dust sample is charged back into the smelting circuit. This process suffers from the drawback that it reduces the plant's production capacity. The main object of the present invention is to provide an improved process for recovery of copper from copper plant dust, which obviates the drawbacks as detailed above. Another object of the present invention is to provide an improved process of sulphuric acid leaching of roasted copper plant dust, so that the resulting copper sulphate solution could be used directly as electrolyte in the copper electrorefming tank. In the process of present invention, copper plant dust is roasted prior to leaching in sulphuric acid. During roasting all the sulphides are converted to oxides CuS + 7/2O2 → CuO.CuSO4 + SO2 (1) CuFeS2 + 13/2 O2 → 2CuO + Fe2 O3 + 4 SO2 (2) The oxides produced during roasting are easily leachable in sulphuric acid and enhance the copper recovery CuO + H2S04 → CuSO4 + H2O (3) CuO. Fe2O3 + 2 H2SO4 →CuSO4 + Fe2 O3 + H2O (4) Accordingly, the present invention provides an improved process for recovery of copper from copper plant dust which comprises i) grinding the copper dust of the composition such as herein described, to about -140µM in size, ii) characterised in that roasting the above ground copper plant dust at a temperature ranging between 600-800°C for a period of 1 to 4 hours, iii) leaching the above roasted ground copper plant dust in sulphuric acid medium with a solid to liquid ratio in the range of 1: 2.5 to 1: 20 at a temperature ranging from 30°C to 80°C, iv) filtering the above said leached slurry and v) recovering copper from the said filtrate by known method. In an embodiment of the present invention the copper plant dust have composition in the range of Cu 35 - 38 % Co 0.052 - 0.058% Fe 15.22-18.45% SiO2: 4.35 - 6.50 % A12O3 : 0.35 - 0.42% S 7.88 - 9.05% Ag: 0.014-0.018% Cd: 0.004-0.008% Zn: 0.152-0.184% Bi : 0.045 - 0.068% Pb: 0.138-0.150% In yet another embodiment the sulphuric acid used for leaching of copper plant dust is of commercial grade In yet another embodiment the concentration of sulphuric acid solution used is in the range of 5-40 % (v/v). According to a feature of this invention, the leach liquor produced on leaching in sulphuric acid of roasted copper plant dust can be used directly as electrolyte in the copper electrorefining plant . By the process of present invention, copper recovered from the leach solution is 95%. Novelty of the present invention is introduction of roasting step prior to leaching, for recovery of copper from copper plant dust. The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention. EXAMPLE-1 5 grams of the copper plant dust sample was leached in 30% (v/v) sulphuric acid at solid to liquid ratio 1: 2.5 at 30°C for 4h. Then the solids were separated from the solution by filtration and was analysed for copper. The recovery of copper obtained was found to be 35.13%. EXAMPLE - II 5 grams of copper plant dust was leached for 4h in 10 % (v/v) sulphuric acid at solid to liquid ratio 1:10 at 30°C. Then the solids were separated from the solution by filtration and was analysed for copper. The recovery of copper obtained was found to be 55%. EXAMPLE -III 10 grams of copper plant dust sample was leached for 4h in 10 % (v/v) sulphuric acid at solid : liquid ratio 1:10 at 60°C. Then the solids were separated from the solution by filtration and was analysed for copper. The recovery of copper obtained was found to be 67.05%. EXAMPLE - IV 5 grams of copper plant dust sample was leached for 4h at 80°C in 10 % (v/v) sulphuric acid at solid to liquid ratio 1:10. Then the solids were separated from the solution by filtration and was analysed for copper. The recovery of copper obtained was found to be 75%. EXAMPLE - V 5 grams of the copper plant dust sample was roasted at 600°C for 4h. The roasted product was leached in 10 %(v/v) sulphuric acid at solid : liquid ratio 1:10 at 30°C for 4h. Then the solids were separated from the solution by filtration and was analysed for copper. The recovery of copper obtained was found to be 95%. EXAMPLE -VI 5 grams of the copper plant dust sample was roasted at 700°C for 4h. The roasted product was leached in 10 %(v/v) sulphuric acid at solid : liquid ratio 1:10 at 30°C for 4h. Then the solids were separated from the solution by filtration and was analysed for copper. The recovery of copper obtained was found to be 90.9%. EXAMPLE -VII 5 grams of the copper plant dust sample was roasted at 800°C for 4h. The roasted product was leached in 10 %(v/v) sulphuric acid at solid : liquid ratio 1:10 at 30°C for 4h. Then the solids were separated from the solution by filtration and was analysed for copper. The recovery of copper obtained was found to be 82.7%. The main advantages of the present invention are (i) In the present invention consumption of energy is less than the conventional pyrometallurgical process as it excludes further smelting step, (ii) In the present invention sulphuric acid is used as the leaching medium and hence the process is technically feasible due to less corrosion problem, (iii) The present invention has resulted in recoveries of copper about 95% . (iv) In the present invention leach liquor contains less impurities, (v) Composition of leach liquor is comparable with electrolyte used for electrorefining tank and therefore, the leach liquor can be directly used in the electrorefining plant without further purification, (vi) In the present invention the capital investment cost of the process is less. We claim 1. An improved process for recovery of copper from copper plant dust which comprises, i) grinding the copper dust of the composition such as herein described, to about -140 µm in size, ii) characterised in that roasting the above ground copper plant dust at a temperature ranging between 600-800°C for a period of 1 to 4 hours, iii) leaching the above roasted ground copper plant dust in sulphuric acid medium with a solid to liquid ratio in the range of 1: 2.5 to 1: 20 at a temperature ranging from 30°C to 80°C, iv) filtering the above said leached slurry and v) recovering copper from the said filtrate by known method. 2. An improved process as claimed in claims 1 to 3 wherein the concentration of sulphuric acid solution used is in the range of 5 - 40 % (v/v). 3. An improved process for the recovery of copper from copper plant dust substantially as herein described with reference to the examples.

Documents:

1012-del-2001-abstract.pdf

1012-del-2001-claims.pdf

1012-del-2001-correspondence-others.pdf

1012-del-2001-correspondence-po.pdf

1012-del-2001-description (complete).pdf

1012-del-2001-form-1.pdf

1012-del-2001-form-18.pdf

1012-del-2001-form-2.pdf

1012-del-2001-form-3.pdf