WO2014061037A1

WO2014061037A1 - Treatment of hazardous solid waste generated in copper manufacturing process

Info

Publication number: WO2014061037A1
Application number: PCT/IN2013/000635
Authority: WO
Inventors: Manmohan Kulkarni SADGURU; Vasant Chavan SANDEEP; Ravindra Kini HARSHAD
Original assignee: Hindalco Industries Limited; Aditya Birla Science & Technology Company Limited
Priority date: 2012-10-18
Filing date: 2013-10-18
Publication date: 2014-04-24

Abstract

The present invention relates to a method for treatment of solid waste generated in copper manufacturing process comprising treating the solid waste with a mineral acid. It further relates to the recovery of transition and post transition metals and arsenic from the solid waste.

Description

TITLE OF THE INVENTION

Treatment of hazardous solid waste generated in copper manufacturing process

FIELD OF THE INVENTION

The present invention relates to a method for treatment of solid waste generated in copper manufacturing process. It further relates to the recovery of transition and post transition metals and arsenic from the solid waste.

BACKGROUND OF THE INVENTION

The effluent treatment in copper manufacturing process leads to the generation of large quantities of hazardous solid waste. This hazardous waste has conventionally been precipitated out in the form of waste gypsum by using Calcium hydroxide, Strontium hydroxide or Barium hydroxide. The hazardous nature of this waste is primarily due to the presence of large arsenic content in the range of 0.1 to 0.5 % or more. The conventional known method for disposing this waste is in the form of secured landfill.

A major concern of this waste is that substantial amount of valuable copper and other transition and post transition metals gets lost by being trapped in the disposed waste. Thus, along with copper, lesser quantities of other transition metals such as Iron, Nickel, Zinc etc. and post- transition metals such as aluminium, gallium, Indium etc. also are wasted as part of the hazardous solid waste. There is thus a need for a novel process for treatment of solid waste generated during copper manufacturing and also for a process for the recovery and maximum retrieval of transition and post-transition metals from said solid waste. DESCRIPTION OF THE INVENTION

According to the invention there is provided a process for treatment of solid waste generated during copper manufacture comprising the step of treating said solid waste with a mineral acid. The concentration of the mineral acid is from 0.1 - 20%. The mineral acid is selected from at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, hydrofluoric acid, hydrobromic acid and/or perchloric acid. This acid treatment aids in leaching out transition metals such as copper, Nickel, Zinc, Cobalt, etc., post-transition metals such as aluminium, gallium, Indium etc. and arsenic into an aqueous acidic solution. The mineral acid is selected from at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, hydrofluoric acid, hydrobromic acid and/or perchloric acid.

The method further includes the recovery of the transition and post-transition metals and arsenic from the acidic solution comprising the step of selectively precipitating out the transition and post-transition metals and arsenic with a precipitating agent selected from among any water soluble metal sulphide or hydrogen sulfide. Thus, the transition and post-transition metals and arsenic is precipitated out in the form its sulfides. Alternatively, the recovery of the transition and post-transition metals and arsenic can also be carried out using any of the conventionally known methods. The process of recovery involves addition of effective amount of metal or hydrogen sulfide solution as the precipitating agent to the effluent under vigorous stirring. The sodium sulfide solution concentration used was controlled as a function of copper concentration. The sodium sulfide used was in the range of 80 to 120% of the stoichiometric amount required to precipitate Cu as CuS. After precipitation of copper as a sulfide, it can be recycled back to the smelter for further copper recovery. Any arsenic or other heavy element species that also go into the solution along with copper are then selectively precipitated. The removal of arsenic involves precipitating with metal or hydrogen sulfide. The sulfide is added at a slow rate to the solution under stirring with a larger residence time of about 2 h. The amount of sulfide required is about 2-3 times of stoichiometric amount of arsenic, considering the formation of the precipitating species to be As₂S₃. Excess sulfide is required as some amount is lost due to its reaction with the acid to form ¾S. This solid As-precipitate formed is disposed off at secured landfills in appropriate manner due to its inherent toxic nature. Finally, the excess acid is reused as a leaching agent for further dissolution of copper in the solid waste or subsequently neutralized using lime or other base to form gypsum.

In an alternative embodiment, the novel process of treatment of solid waste generated during copper manufacture comprises the step of treating the solid waste with acidic effluent generated during copper manufacture process. Thus, in this case the leachant used is the acid effluent arising from copper manufacturing process itself. The concentration of acid in the acid effluent is in the range of 0.1-20%. The acid effluent also contains some copper (1000-4000 ppm), arsenic (500-3000 ppm) along with other transition and post-transition metals such as Iron, Nickel, Zinc, Sodium, Calcium, Magnesium, Aluminium, etc. The acid effluent can be reused a number of times for treatment of the solid waste for copper dissolution before its final neutralization with lime.

In 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 if the precipitate such as Copper sulphide or Arsenic sulphide. The flocculating agent is typically a long chain polymer such as polyacrylamides. The present invention thus also relates to a process for recovery of transition and post-transition metals from hazardous waste in a safe manner to address the hazards associated with various processing stages.

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 10 g of hazardous solid gypsum was taken in a beaker. To this solid about 100 ml of 10% sulfuric acid as a leachant was added and stirred for a period of 15-20 min. This resulted in dissolution of arsenic as well as transition and post-transition metals such as Iron, Nickel, Zinc, Aluminium, copper etc. from the solid waste into the acid solution as given in Table-I below:

Table-I:

Once into solution; sodium sulfide solution (10%) was added to this aqueous acid solution under stirring. (The amount of sodium sulfide added was calculated based on the amount of copper present in the aqueous acid solution.) The stirring was continued for about 5 min. and the solution was filtered. A solid precipitate essentially of copper along with minor impurities of Arsenic and other heavy metals was obtained. This separated copper precipitate can be recycled to copper manufacturing plant for copper recovery.

Example 2:

In this example, about 10 g of hazardous solid was taken in a beaker. In this case the leachant used was the effluent from the plant instead of fresh sulfuric acid used in previous example. The plant effluent itself contains sulfuric acid in the range of 1 to 20% and hence can be used as a leachant. Thus about 100 ml of effluent stream from copper manufacturing plant was added to the beaker and the contents were stirred for about 15-20 min.

The initial concentration of copper and arsenic in the effluent were determined to be about 3075 ppm and 851 ppm respectively. After leaching of gypsum with this effluent, the concentration of copper in the effluent solution increased to about 4982 ppm and that of arsenic increased to about 1663 ppm. Further, the copper was recovered from this solution by precipitating as sulfide using stoichiometric amount of sodium sulfide. In this step a complete copper recovery was achieved with copper concentration in the solution being reduced to < 1 ppm. Further, the arsenic was removed from this solution by sodium sulfide. The sodium sulfide added was about 2.5 times of stoichiometric requirement. In this step, near complete removal of arsenic was achieved with residual arsenic in the solution as about 1.71 ppm. Further, the solution was treated with lime for neutralization of the acid. After the lime treatment the copper in the solution was < 1 ppm whereas the arsenic was about 0.21 ppm. Example-3:

In this example, the effect of acid concentration on the leaching efficiency was investigated. Thus, about 10 gm of gypsum were taken individually in four different beakers. To each of the beakers 100 ml of different acid (sulfuric acid) concentrations viz., 2%, 5%, 10% and 20% were added resulting in respective samples as G-2%, G-5%, G-10%, G-20% . The gypsum and acid mixture in each beakers were then stirred for 15 min. This resulted in dissolution of arsenic as well other metals such as Iron, Nickel, Zinc, Copper etc. from the solid gypsum into the acid medium. The solution were then filtered and analysed for determining the amount of various species transferred from gypsum into the solution. The results are tabulated in Table-II below:

Table-II

Example-4:

In this example also, the effect of acid concentration on the leaching efficiency was investigated. However, the acid concentrations used were lower than 2% as used in the previous example. Thus, about 10 gm of gypsum were taken individually in three different beakers. To each of the beakers about 100 ml of different acid (sulfuric acid) concentrations viz., 0.2%, 0.5%, 1.0% were added resulting in respective samples as G-0.2%, G-0.5% and G-1.0% respectively. The gypsum and acid mixture in each beakers were then stirred for 15 min. This resulted in dissolution of arsenic as well other metals such as Iron, Nickel, Zinc, Copper etc. from the solid gypsum into the acid medium. The solution were then filtered and analysed for determining the amount of various species transferred from gypsum into the solution. The results are tabulated in Table-Ill below:

Table-Ill:

Example-5:

In this example, the effect of residence time on the leaching efficiency was investigated. Thus, about 10 gm of gypsum was taken individually in three different beakers. To each of the beakers about 100 ml of concentrated sulfuric acid was added. The gypsum and acid mixture in each beakers were then stirred for varying time intervals as 5 min, 15 min and 30 min, resulting in samples G-5 min, G-15 min and G-30 min, respectively. This resulted in dissolution of arsenic as well other metals such as Iron, Nickel, Zinc, Copper etc. from the solid gypsum into the acid medium. The solution were then filtered and analysed for determining the amount of various species transferred from gypsum into the solution. The results are tabulated in Table-IV below:

Table-IV:

Example-6:

In this example, the use of nitric acid as a leachant instead of sulfuric acid was investigated. Thus, about 10 gm of gypsum was taken in a beaker. To this beaker about 100 ml of 20 % nitric acid was added. The gypsum and acid mixture in each beakers were then stirred for 30 min resulting in samples as G-HN03. This resulted in dissolution of arsenic as well other metals such as Iron, Nickel, Zinc, Copper etc. from the solid waste into the acid medium. The solution were then filtered and analysed for determining the amount of various species transferred from gypsum into the solution. The results are tabulated in Table-V below: Table-V

Example-7:

In this example, the use of hydrochloric acid as a leachant instead of sulfuric acid was investigated. Thus, about 10 gm of gypsum was taken in a beaker. To this beaker about 20% hydrochloric acid was added. The gypsum and acid mixture in the beaker was then stirred for 30 min resulting in samples as G-HCl. This resulted in dissolution of arsenic as well other metals such as Iron, Nickel, Zinc, Copper etc. from the solid waste into the acid medium. The solution were then filtered and analysed for determining the amount of various species transferred from gypsum into the solution. The results are tabulated in Table- VI below:

Table- VI:

Copper Iron Nickel Zinc Arsenic

(ppm) (ppm) (ppm) (ppm) (ppm)

G-HCl 1494 156 23 95 422 Example-8:

In this example the leaching of gypsum was carried in multiple steps so as to achieve maximum removal of arsenic from gypsum. Thus, about 10 gm gypsum was taken in three different beakers. To each of the beakers about 100 ml of 0.2%, 0.5% and 1.0% sulfuric acid were added respectively to each beaker. The gypsum and acid mixture was then stirred for about 30 min. and then filtered. The residual solid gypsum in each case was then separated and transferred to another set of three beakers. About 100 ml of 50% sulfuric acid was then added to each of these individual solutions. The mixtures in each beakers were then stirred for about 30 mins and filtered. Thus, the separated solid gypsum were further treated for additional step of acid leaching. Here, each of the three samples were again treated with about 100 ml of 50% sulfuric acid solution. The solution was filtered and the residual gypsum solid was separated and washed thoroughly with distilled water. The residual solid samples in each case were then digested using concentrated HN03 and were analysed for arsenic content. In each of the three treated gypsum samples the arsenic content was reduced to < 1 ppm.

Claims

Claims:

1. A method for treatment of solid waste generated during copper manufacture process comprising treating the solid waste with a mineral acid.

52. The method for treatment of solid waste as claimed in claim 1, wherein the concentration of the mineral acid is 0.1 - 20%.

3. The method for treatment of solid waste as claimed in claim 1 , wherein the mineral acid is

selected from at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid,

10 hydrofluoric acid, hydrobromic acid and/or perchloric acid.

4. The method for treatment of solid waste as claimed in claim 1 , further comprising addition of water soluble sulfide or hydrogen sulfide to an acidic solution obtained on treatment of the solid waste with the mineral acid, to selectively precipitate out metal sulfides and/or arsenic sulfide.

15

5. The method for treatment of solid waste as claimed in claim 4, wherein the method further comprises adding a flocculating agent for precipitation of the metal sulfide and/or arsenic sulfide.

206. A method for treatment of solid waste generated during copper manufacture comprising treating said solid waste with acidic effluent generated during copper manufacture process.

7. The method for treatment of solid waste as claimed in claim 6, wherein the concentration of the acid in the acidic effluent is 0.1 - 20%. The method for treatment of solid waste as claimed in claim 6, further comprising addition of water soluble sulfide or hydrogen sulfide to an acidic solution obtained on treatment of the solid

.

waste with the acidic effluent, to selectively precipitate out metal sulfides and/or arsenic sulfide.

The method for treatment of solid waste as claimed in claim 8, wherein the method further comprises adding a flocculating agent for precipitation of the metal sulfide and/or arsenic sulfide.