FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
As amended by the Patents (Amendment) Act, 2005
&
THE PATENTS RULES, 2003
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
A novel process for treatment of effluent from copper manufacturing process
APPLICANTS
Hindalco Industries Limited, 3rd Floor, Century Bhavan, Dr Annie Besant Road, Worli,
Mumbai - 400030, Maharashtra, an Indian Company
and
Aditya Birla Science & Technology Company Limited, Aditya Birla Centre, 2nd Floor, C
Wing, S K Ahire Marg, Worli, Mumbai 400025, Maharashtra, an Indian Company
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes this invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
The present invention relates to a novel process for recovery of copper from the effluent generated during copper manufacturing process. The invention further relates to removal of heavy metal hazardous waste from the effluent and/or the decontamination of the effluent containing heavy metals. The process also relates to recovery of gypsum and purified water from the effluent generated during copper manufacturing process, wherein the purified water is recycled back for the copper manufacturing process.
BACKGROUND OF THE INVENTION
Most of the metal manufacturing processes generate large volumes of effluent streams and solid wastes. Much of these wastes are hazardous in nature, since they contaminate the surface and ground water through the leachate generated at the dump-sites causing direct threat to environment and health. Amongst the heavy and toxic metals, arsenic, cadmium, chromium, nickel, lead, copper, mercury and zinc are considered deleterious to the environment, when their concentrations are more than the stipulated limits.
In the context of metal extraction and refining industry, the Copper manufacturing process leads to the generation of large quantities of aqueous effluent. This effluent primarily contains copper and arsenic along with lesser quantities of other heavy elements such as Iron (Fe), Nickel (Ni), Zinc (Zn) etc. The heavy metals such as Fe, Mi, Zn although are typically present in quantities < 500 ppm, are yet high enough to be considered as environmental hazard. However, the much bigger concern is the presence of copper (Cu) and arsenic (As). The copper concentration in the effluent streams may be typically be in the range of 500 ppm to 4000 ppm. In some cases a part of the effluent streams may also have concentrations of copper as high as 10000 ppm. Thus, the

high Cu content posses a major challenge in terms of environmental concerns as well as value loss associated with copper. Further, the presence of highly toxic arsenic in the effluent stream makes the disposal and treatment of the effluent a major challenge. The arsenic content in the. effluent stream is substantially higher in the range of 500 ppm to 3000 ppm. In addition, the effluent is high in acid content, especially when associated with production of sulfuric acid from the waste SO2 emission during the copper smelting processes. The process generally adopted by copper manufacturers is to treat the effluent with lime so as to precipitate various contaminants, viz. Cu, As Fe, Ni, Zn etc. followed by formation of gypsum due to neutralization of the acid with the lime. The gypsum thus formed, contains precipitates of arsenic and various other heavy elements making the entire quantity as hazardous waste. In addition, the copper in the effluent also gets trapped as part of the hazardous waste resulting in considerable value loss.
Some of the chemical treatment methods have been found to be generally effective for the removal of heavy metals. For example, limestone, hydroxides, carbonates, and sulfides have been described in prior art to remove heavy metals from aqueous solutions through chemical reactions (Treatability Manual, Vols. 1-5, Monsanto Research Corporation, EPA 600 8 80 042a, July, 1980). Also, Sulfide precipitation of heavy metals has been reported to be an effective alternative to hydroxide and other precipitation methods (R. W. Peters and Y. Ku, "Batch Precipitation Studies For Heavy Metal Removal By Sulfide Precipitation", AIChE Symposium Series No. 243, Vol. 81). Conventional sulfide precipitation processes have been performed at ambient temperature and are limited to the treatment of wastewater containing little or no organic materials and complex compounds (D. Bhattacharyya et ah, "Precipitation of Heavy Metals with Sodium Sulfide: Bench Scale and Full Scale Experimental Results" AIChE Symposium No. 209,

Vol. 77). Other prior disclosures of sulfide precipitation of heavy metals from soiution include, for example U.S. Pat. Nos. 4,503,017 and 4,652,380.
However, these prior art processes add the sulfide to the effluent in a non controlled manner. Thus, these processes results in simultaneous precipitation of species such as Cu and As. There is no measure for selectively removing copper from the effluent stream. Further, there are additional steps of sodium hydroxide or other base addition for increasing the pH, which increases the cost of the process. The other heavy elements such as Fe, Ni, Zn, Co etc. are also removed by Na2S to precipitate as metal sulfides at increased pH, resulting in further increase in the cost of the process due to consumption of Na2S. Also, the use of Na2S for precipitation of all heavy elements results in formation of toxic H2S due to reaction of Na2S and acid. Further, these prior art processes are for treatment of lower concentration of the various heavy element species typically < 500 ppm for Cu, Fe, Ni, Zn etc., whereas the effluent from the copper manufacturing has higher concentrations of these species along with a higher acid content.
Moreover, it has been observed that large quantities of effluent from the industrial processes are being wasted because of the presence of heavy metals and the toxic nature of the effluent.
Accordingly, there has been a need to develop an effective method especially from the copper manufacturing industry for making the effluent reusable and for recycling the same into industrial processes by recovery of copper from the waste effluent as well as for removal of arsenic from the effluent and further treatments.

DESCRIPTION OF THE INVENTION
According to the invention there is provided a method for treating an effluent generated in a
copper-manufacturing plant comprising the steps of:
(a) controlled addition of water soluble sulfide or hydrogen sulfide to the effluent to selectively precipitate out copper sulfide (CuS), wherein the stoichiometric ratio of copper to sulfide ions is in the range of 1:0.9 to 1:1.2; (b) controlled addition of water soluble sulfide or hydrogen sulfide to the effluent obtained from step (a) to selectively precipitate out arsenic sulfide (As2S3)wherein the stoichiometric ratio of arsenic to sulfide ions is in the range of 1.1 to 3.0; and (c) controlled addition of lime to the effluent obtained from step (b) to precipitate out gypsum.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
According to the invention, there is provided a method of purifying industrial waste aqueous effluent, specifically effluent generated from copper manufacturing process.
According to the invention, there is provided a method for treating an effluent generated in a
copper-manufacturing plant comprising the steps of:
(a) controlled addition of water soluble sulfide or hydrogen sulfide to the effluent to selectively precipitate out copper sulfide (CuS), wherein the stoichiometric ratio of copper to sulfide ions is in the range of 1:0.9 to 1:1.2; (b) controlled addition of water soluble sulfide or hydrogen sulfide' to the effluent obtained from step (a) to selectively precipitate out arsenic sulfide (AS2S3) wherein the stoichiometric ratio of arsenic to sulfide ions is in the range of 1.1 to 3.0; and (c) controlled addition of lime slurry to the effluent obtained from step (b) to precipitate out gypsum.

An embodiment of the invention relates to a method for selective extraction of heavy metals in different steps via sulfide precipitation.
Another embodiment of the invention relates to a process for treatment of aqueous acidic effluent from copper manufacturing/refining process whereby the copper, arsenic and gypsum are selectively precipitated so as to minimize the hazardous waste in the effluent. The selective precipitation of copper is carried out by treating the acidic effluent generated in copper manufacturing process with a water soluble metal sulphide or hydrogen sulphide by controlled, gradual addition of sulfide. Further, the invention relates to selectively extracting ail of the copper, even from a high copper concentration effluent (copper concentration 1000-4000ppm) so that the copper concentration in the effluent is reduced to < Ippm.
Next, the selective precipitation of arsenic is carried out by treating the acidic effluent remaining after the copper removal with a water soluble metal sulphide or hydrogen sulphide. Large quantities of arsenic is selectively precipitated out from a high arsenic concentration effluent (500-3000 ppm arsenic and in the presence of other heavy metals such as iron, nickel, zinc etc). The arsenic concentration in the treated effluent is reduced by upto < 10 ppm.
fn a further embodiment of the present invention, the precipitation of various species such as Copper, Arsenic etc may be further enhanced by use of a flocculant. The flocculating agent can be added after addition of sodium sulphide, resulting in improved precipitation and settling of the precipitate. The flocculating agent is typically a long chain polymer such as polyacrylamides.

Finally, the acidic effluent is neutralized by addition of lime. The acidic content of the effluent is reduced to < 0.1% from about 1-10 %. Addition of lime to the acidic effluent, remaining after the copper and arsenic removal, precipitates out the gypsum. The heavy elements such as Fe, Ni, Zn, Co etc. are also removed by the lime.
In an embodiment, the precipitated copper is filtered followed by washings with water to remove the acid adsorbed/associated with the solid precipitate. The washed copper sulfide precipitate is then dried and recycled back to the copper manufacturing plant for value generation,
In another embodiment of the process, the H2S formed during removal of arsenic is used as additional precipitating agent for precipitating the copper in the first step. Thus, in the present case the H2S formed was passed through a fresh effluent sample resulting in further precipitation of copper sulfide.
In yet another embodiment, the Gypsum formed on addition of lime to the effluent can be considered as non hazardous and after appropriate processing can be used as commercial grade gypsum in various industries such as cement industry etc.
Further, the non hazardous effluent stream obtained after removal of the heavy metals may be subjected to reverse osmosis (RO) plant to purify the water which can be recycled back to the plant.
In a specific embodiment, the experimental method involves determining the content of copper, arsenic and other heavy element in the effluent by means of suitable analytical technique such as

JCP followed by measuring appropriate amount of effluent stream in a vessel. The acid content of this effluent stream is adjusted to be in the range 1% to 15%. The heavy metal contents of the effluent stream are measured. Then adequate quantity of sodium sulfide based on copper to sulfide ratio as 1:0.9 to 1:1.2 (molar ratio) is measured and gradually added to the effluent stream under continuous stirring. This measured quantity of sodium sulfide can be added as a solution in water or directly by adding solid flakes of sodium sulfide. Further, the entire solution is stirred for duration of 0.1 min to 15 min. This results in the formation of CuS precipitate. A flocculating agent is optionally added to the precipitate and the solid CuS is filtered out from the effluent. Then, adequate quantity of sodium sulfide based on arsenic to sulfide ratio asl.l to 3.0 (molar ratio) is measured and gradually added to the effluent stream under continuous stirring. Further, the entire solution is stirred for duration of 10 min to 2 hrs, This results in the formation of arsenic sulfide precipitate. A flocculating agent is optionally added to the precipitate and the solid arsenic sulfide is filtered out from the effluent. Further, a lime slurry (20%) in water is prepared and gradually added to the effluent under stirring till a pH in the range of 6-7 is obtained. This results in the formation of a solid gypsum precipitate due to reaction of lime and acid of the effluent. Again, a flocculating agent is added and the solid gypsum is filtered out from the effluent.
The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of

description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
EXAMPLES
The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
Example-1: About 250 ml of effluent containing about 3635 ppm Cu, 2351 ppm As, 185 ppm Fe, 422 ppm Ni, 129 ppm Zn are taken in a beaker. About 250 ml of distilled water is added to the effluent to prepare a diluted effluent stock solution of 500 ml. Further, 50ml of the stock solution was taken in each of 9 volumetric flasks (250ml). In this each flask, varying concentrations (0ml, 5ml, 10ml, 20ml, 35ml, 50ml, 65ml, 80ml. 100ml) of 1% sodium sulfide was added under continuous stirring, which resulted in the spontaneous formation of black color precipitate. Each treatment was carried with continuous stirring duration of 1 min. After the completion of reaction (stirring), the treated effluent was further diluted with 250ml of distilled water and was filtered using Whatman 41 filter paper. The diluted solution was then subjected to analysis content using 1CP.

Table-]; Change in concentration of species in Effluent by precipitation

Sample Amount of 1% sulfide added (ml) Arsenic (ppm) Copper (ppm) Iron (ppm) Nickel (ppm) Zinc (ppm)
Sample l(std) 0 235.16 363.54 18.58 42.23 12.91
Sample 2 5 226.53 281.87 18.23 41.77 11.98
Sample 3 10 219.2 208.81 18.13 41.78 11.52
Sample 4 20 210.45 65.19 18.32 41.85 10.45
Sample 5 35 159.31 <0.1 18.73 41.45 9.86
Sample 6 50 156.43 <0.1 18.32 41.54 11.19
Sample 7 65 154.11 <0.1 17.94 4.32 9.61
Sample 8 80 145.48 <0.1 18.3 41.29 9.48
Sample 9 100 146.04 <0.1 17.85 38.96 9.34
Thus, the addition of specific amount of sodium sulfide solution resulted in selective extraction of Cu resulting in < 1 ppm Cu in the effluent resulting in > 99% Cu extraction as CuS precipitate. The concentrations of other metal species such as Fe, Ni, Zn are practically unaltered.
Example-2:
About 250 ml of effluent containing about 3795 ppm Cu, 2105 ppm As, 203 ppm Fe, 465 ppm Ni, 140 ppm Zn are taken in a beaker. About 250 ml of distilled water is added to the effluent to. prepare a diluted effluent stock solution of 500 ml. Further, 50ml of the stock solution was taken in each of 9 volumetric flasks (250ml). In this each flask, varying concentrations (0ml, 5ml, 10ml, 20ml, 35ml, 50ml, 65ml, 80ml, 100ml) of 1% sodium sulfide was added under continuous stirring, which resulted in the spontaneous formation of black color precipitate. Each treatment was carried with continuous stirring duration of 1 min. After the completion of reaction (stirring), the treated effluent was further diluted with 250ml of distilled water and was filtered

using Whatman 41 filter paper. The diluted solution was then subjected to analysis content using ICP and the results are shown in Table-2 below. Further, the treated effluent was kept overnight, which resulted in further yellow precipitate. This solution was filtered using Whatman 41 filter. paper and then subjected to Arsenic content using ICP as shown in Table-2 below.
Table-2: Change in concentration of species in Effluent by precipitation

Sample Amount of 1% sulfide added (ml) Arsenic (ppm) (overnight) Copper (ppm) Iron (ppm) Nickel (ppm) Zinc (ppm)
Sample l(std) 0 210.531 379.55 20.379 46.55 14.021
Sample 2 5 201.531 295.7 20.194 45.19 11.343
Sample 3 10 194.318 220.252 19.865 45.318 10.532
Sample 4 20 176.232 57.107 19.529 44.119 9.085
Sample 5 35 129.288 <0.] 19.706 44.159 8.469
Sample 6 50 102.069 <0.1 17.615 36.957 9.563
Sample 7 65 90.02 <0.1 18.35 39.411 10.582
Sample 8 80 59.643 <0.1 18.789 40.011 10.873
Sample 9 100 26.648 <0.1 18.05 36.235 10.212
Thus, the addition of specific amount of sodium sulfide solution resulted in selective extraction of Cu resulting in < 1 ppm Cu in the effluent resulting in > 99% Cu extraction as CuS precipitate. The concentrations of other metal species such as Fe, Ni, Zn are practically unaltered.
Example 3: About 250 ml of effluent containing about 3051 ppm Cu, 491 ppm As, 117 ppm Fe, 87 ppm Ni, 74 ppm Zn are taken in a beaker. About 250 ml of distilled water is added to the effluent to prepare a diluted effluent stock solution of 500 ml. Further, 50ml of the stock solution was taken

in each of 9 volumetric flasks (250ml). In this each flask, varying concentrations (0ml, 5ml, 10ml, 20ml, 35ml, 50ml, 65ml, 80ml, 100ml) of 1% sodium sulfide was added under continuous stirring, which resulted in the spontaneous formation of black color precipitate. Each treatment was carried with continuous stirring duration of 1 min. After the completion of reaction (stirring), the treated effluent was further diluted with 250ml of distilled water and was filtered using Whatman 41 filter paper. The diluted solution was then subjected to analysis using ICP and the results are shown in Table-3 below. Further, the treated effluent was kept overnight, which resulted in further yellow precipitate. This solution was filtered using Whatman 41 filter paper and then subjected to Arsenic measurement using ICP as shown in Table-3 below.
Table-3: Change in concentration of species in Effluent by precipitation

Sample Amount of sulfide added (ml) Arsenic (ppm) (Overnight) Copper (ppm) Ferrous (ppm) Nickel (ppm) Zinc (ppm)
Sample 1 (std) 0 49.178 305.124 11.729 8.732 7.409
Sample 2 10 44.187 234.864 13.246 8.797 7.14
Sample 3 20 36.677 163.273 12.928 9.021 8.915
Sample 4 40 5.598 1.304 12.556 10.574 7.61
Sample 5 70 0.048 <0.1 12.798 9.919 7.606
Sample 6 100 0.01 <0.1 12.366 9.403 7.227
Sample 7 130 <0.1 <0.1
Sample 8 160 <0.1 ' <0.1 12.251 8.877 6.922
Sample 9 200 <0.1 <0.1 12.247 8.795 6.981
Thus, the addition of specific amount of sodium sulfide solution resulted in selective extraction of Cu resulting in < 1 ppm Cu in the effluent resulting in > 99% Cu extraction as CuS precipitate. Also, the addition of specific amount of sodium sulfide solution resulted in selective extraction of As resulting in < 1 ppm As in the effluent and in > 99% As extraction as arsenic

sulfide precipitate. The concentrations of other metal species such as Fe, Ni, Zn are practically unaltered.
Example 4 About 250 ml of effluent containing about 644 ppm Cu, 259 ppm As, 140 ppm Fe, 124 ppm Zn are taken in a beaker. About 250 ml of distilled water is added to the effluent to prepare a diluted effluent stock solution of 500 ml. Further, 50ml of stock solution was taken in each of 9 volumetric flasks (100ml). In this each flask, varying concentrations (0ml, 0.5ml, 1ml, 1.5ml, 2ml, 2.5ml, 3ml, 3.5ml, 4ml) of 1% sodium sulfide was added, which resulted in the spontaneous formation of black color precipitate. Each treatment was carried with continuous stirring for 1 min. After the completion of reaction (stirring), the treated effluent was further diluted with 100 ml of distilled water and was filtered using Whatman 41 filter paper. The diluted solution was then subjected to analysis using ICP and the results are shown in Table-4 below. Further, the treated effluent was kept overnight, which resulted in further yellow precipitate. This solution was filtered using Whatman 41 filter paper and then subjected to Arsenic measurement using ICP as shown in Table-4 below.

Table-4: Change in concentration of species in Effluent by precipitation

Sample Amount of sulfide added (ml) Arsenic
(ppm)
overnight Copper (ppm) Ferrous (ppm) Nickel (ppm) Zinc
(ppm)
Sample 1 (std) 0 25.985 64.438 14.09 0.038 12.97
Sample 2 0.5 24.118 49.13 14.12 0.047 12.95
Sample 3 1.0 22.977 31.819 14.37 0.04 13.16
Sample 4 1.5 21.242 13.126 14.34 0.039 13.17
Sample 5 2.0 15.213 <0.1 14.15 0.038 12.98
Sample 6 2.5 4.854 <0.1 14.35 0.054 13.09
Sample 7 3.0 2.261 <0.1 14.53 0.048 13.28
Sample 8 3.5 1.709 <0.1 14.52 0.052 13.17
Sample 9 4.0 1.391 <0.1 14.46 0.041 13.19
Thus, the addition of specific amount of sodium sulfide solution resulted in selective extraction of Cu resulting in < 5 ppm Cu in the effluent resulting in > 99% Cu extraction as CuS precipitate. The concentrations of other metal species such as Fe, Ni, Zn are practically unaltered.
Example5: About 250 ml of effluent containing about 644 ppm Cu, 259 ppm As, 140 ppm Fe, 124 ppm Zn are taken in a beaker. About 250 ml of distilled water is added to the effluent to prepare a diluted effluent stock solution of 500 ml. Further, 50ml of stock solution was taken in each of 9 volumetric flask (100ml). In this each flask, varying concentrations (0ml, lml, 2ml, 3ml, 4ml, 5ml, 6ml, 7ml, 8ml) of 1% sodium sulfide was added, which resulted in the spontaneous formation of black color precipitate. Each treatment was carried with continuous stirring for 1

min. After the completion of reaction (stirring), the treated effluent was further diluted with 100ml of distilled water and was quickly filtered using Whatman 41 filter paper. The diluted solution was then subjected to analysis using ICP and the results are shown in Table-5 below. Further, the treated effluent was kept overnight, which resulted in further yellow precipitate. This solution was filtered using Whatman 41 filter paper and then subjected to Arsenic measurement using ICP as shown in Table-5 below.
Table-5: Change in concentration of species in Effluent by precipitation

Sample Amount of sulfide added (ml) Arsenic (ppm) Copper (ppm) Ferrous (ppm) Nickel (ppm) Zinc (ppm)
Sample 1 (std) 0 8.319 181.2 3.11 2.56 1.01
Sample 2 1 7.327 163.3 3.09 2.43 0.99
Sample 3 2 6.732 138.1 2.99 2.46 1.03
Sample 4 3 6.421 87.4 3.01 2.41 1.02
Sample 5 4 15.213 36.4 3.07 2.39 1.01
Sample 6 5 4.53 1.2 2.97 2.53 0.97
Sample 7 6 2.11 <0.1 2.95 2.56 0.93
Sample 8 7 1.603 <0.1 3.09 2.54 0.91
Sample 9 8 1.111 <0A 3.12 2.58 1.06

Stepwise precipitation:
Step-1: Cu precipitation Step-2: As precipitation Step-3: Gypsum precipitation
Step-1: Cu precipitation
About 200ml of effluent was first treated with about 1.72 g of sodium sulfide dissolved in 8.6ml of water. The reaction was carried out in 500ml of glass beaker with magnetic stirring and at room temperature. Addition time for sodium sulfide was 1 min and the treatment was carried with continuous stirring for 5 min. After the completion of reaction (stirring), the treated effluent was filtered using Whatman 41 filter paper under suction. Small amount of sample was subjected to elemental analysis (Cu, Fe, Ni, Zn) using ICP.
Step-2: As precipitation
The treated solution obtained from Cu Precipitation (Step l) was further treated 0.58g of sodium sulfide dissolved in 2.9ml of water, In this case also, the reaction was carried out in 500ml of glass beaker with magnetic stirring and at room temperature. Addition time for sodium sulfide was 1 min and the treatment was carried with continuous stirring for 2 hrs. After the completion of reaction (stirring), the treated effluent was filtered using Whatman 41 filter paper under suction. Small amount of sample was subjected to elemental analysis (Cu, Fe, Ni, Zn) using ICP.
Step-3: Gypsum precipitation
The treated solution obtained from As Precipitation (Step2) was further subjected to lime
treatment. In this, the slurry of lime (around 8g of lime in 50m! of water) was prepared. This

slurry was added to the treated acidic effluent under continuous stirring for the complete neutralization of effluent. The neutralized effluent was filtered using Whatman 42 filter paper under suction. The final filtrate was subjected to elemental analysis (Cu. Fe, Ni, Zn) using ICP.
TabIe-6: Change in concentration of species in Effluent by precipitation

Steps Elemental Species concentrations
Initial Concentration of effluent Copper content Arsenic content 3526ppm 933ppm
Step 1 Copper Precipitation Copper content Arsenic content <0.1ppm 580ppm
Step 2 ' Arsenic Precipitation Copper content Arsenic content <0.1ppm 141ppm
Step 3 Gvpsum Precipitation Copper content Arsenic content <0.1ppm 81ppm
Example 7: In order to completely remove the Arsenic by precipitation, following series of experiment were performed. About 200 ml of effluent solution were taken in a five different beakers. About 9 ml of 10% sodium sulfide solution was added to each under stirring and each of the solutions were filtered to remove the CuS precipitate. After the copper removal the effluent was further treated with increasing amount of sodium sulfide (0 ml, 3ml. 5ml, 7ml, 9ml, and 11ml) to determine the optimum requirement of sodium sulfide for the complete removal of arsenic. Each of these

solutions were allowed to react for about 2h and then filtered and the filtrate analysed by ICP as below.
TabIe-7: Change in concentration of species in Effluent by precipitation

Total amount of sulfide added (ml) Arsenic (ppm) Copper (ppm) Ferrous (ppm) Nickel (ppm) Zinc (ppm)
9m] 364 <0.1 380 354 75
12ml 127 <0.1 382 309 68
14ml 91 <0.1 341 298 66
16ml 26 <0.1 381 295 68
18ml 0.398 <0.1 342 269 65
20ml 0.093 <0.1 332 256 63
It was observed that with addition of about 18 ml of sodium sulfide, the arsenic content in the effluent was reduced to < 1 ppm.
Example 8 Further to demonstrate the process at scale up level (30 kg scale) the following experiment was carried. For this also a typical stepwise precipitation approach was employed,
Stepwise precipitation:
Step-1: Cu precipitation Step-2; As precipitation Step-3: Gypsum precipitation

Step-1: Cu precipitation
About 30 kg of effluent was first treated with 260g of sodium sulfide dissolved in 1.3 litres. The reaction was carried out in 60 liters glass lined reactor with a stirrer and at room temperature. Addition time for sodium sulfide was 5 min and the treatment was carried with continuous stirring of 170rpm for 10 min. After the completion of reaction (stirring), the treated effluent was filtered using centrifuge with 10 microns filter cloth under suction. After the treatment small-amount of sample was subjected to elemental analysis (Cu, Fe, Ni, Zn) using ICP.
Step-2: As precipitation
The treated solution obtained from Cu Precipitation (Stepl) was further treated with 330g sodium sulfide dissolved in 1.65 litres. Here also, the reaction was carried out in 60 liters glass lined reactor with a stirrer and at room temperature. Addition time for sodium sulfide was 5 min and the treatment was carried with continuous stirring for 2 hrs. After the completion of reaction (stirring), the treated effluent was filtered using centrifuge with 10 microns filter cloth under suction. After the treatment small amount of sample was subjected to elemental analysis (Cu, Fe, Ni,Zn) using ICP.
Step-3: Gypsum precipitation
About 1000ml of treated solution obtained from As Precipitation (Step2) was further subjected to lime treatment. Jn this, the slurry of lime (around 20g of lime in 200ml of water) was prepared. This slurry was added to the treated acidic effluent (pH-1.8) under continuous stirring for the complete neutralization (pH-7) of effluent. The neutralized effluent was filtered using Whatman.. 42 filter paper under suction. The final filtrate was subjected to elemental analysis (Cu, Fe, Ni, Zn) using ICP. The complete experimental summary is given below.

TabIe-8; Change in concentration of species in Effluent by precipitation

Scale up trials Arsenic (ppm) Copper (ppm) Ferrous (ppm) Nickel (ppm) Zinc (ppm)
Untreated Effluent 933 3526 482 453 82
Step-1 568 <0.1 366 358 72
Step-2 3.5 <0.1 333 292 65
Step-3 <0.1 <0.1 <0.1 <0.1 <0.1
In this trial it can be observed that copper concentration of < 0.1 ppm is achieved at the end of step-1 suggesting > 99% Cu recovery, in the step -2, the arsenic concentration of < 5 ppm is achieved suggesting > 99% of arsenic removal as well from the effluent stream. The final.. precipitation step by lime addition to the effluent results in practically removal of all the contaminants from the effluent stream.

We claim
1. A method for treating an effluent generated in a copper manufacturing/refining plant
comprising the steps of:
(a) controlled addition of water soluble sulfide or hydrogen sulfide to the effluent to selectively precipitate out copper sulfide (CuS), wherein the stoichiometric ratio of copper to sulfide ions is in the range of 1:0,9 to 1:1.2;
(b) controlled addition of water soluble sulfide or hydrogen sulfide to the effluent obtained from step (a) to selectively precipitate out arsenic sulfide (AS2S3) wherein the stoichiometric ratio of arsenic to sulfide ions is in the range of 1.1 to 3.0; and.
(c) controlled addition of lime slurry to the effluent obtained from step (b) to precipitate out gypsum.

2. The method as claimed in claim 1, wherein the concentration of copper in the effluent is.. in the range of 500 - 4000 ppm.
3. The method as claimed in claim 1, wherein >95% of copper is recovered from the effluent.
4. The method as claimed in claim 1, wherein the concentration of arsenic in the effluent is in the range of 500 - 3000 ppm.

5. The method as claimed in claim 1, wherein >95% of arsenic is recovered from the effluent.
6. The method as claimed in claim 1, wherein the method further comprises adding a flocculating agent in steps a) to c) for precipitation and filtration of the heavy metal sulfide.
7. The method as claimed in claim 1, wherein the copper sulfide precipitated out in step a) is filtered, washed, dried and recycled to the copper manufacturing/refining plant.
8. The method as claimed in claim 1, wherein the pH of the effluent is <3 in steps a) and b).