DESC:FIELD OF THE INVENTION

[001] The present invention relates to a process for treatment of dore slag. In particular, the invention relates to recovery of precious metals from dore slag from TROF (Tilting Rotating Oxy-Furnace).

DESCRIPTION OF THE BACKGROUND ART

[002] Precious metals such as platinum, gold, ruthenium, iridium are of significant importance. Apart from mining, electrolytic refinery slimes are also a major source of precious metals. In copper industry, during the process of electro refining, undissolved metals, oxides and impurities deposit at the bottom of an electrolytic pot cell and forming an anodic slime. Anode slimes from copper refining contains precious metals such as Au, Ag, Pb, Sb, Bi and Te etc.

[003] The anode slime, apart from the various impurities such as Au, Ag, Sb, Se, Bi, Pb also contains copper, which is removed by reacting with sulphuric acid and oxygen. The recovered copper is generally recycled back to copper smelter. The residue of anode slime obtained after removal of copper is decopperised anode slime which is transported to Precious Metal Recovery (PMR) section.

[004] Selenium from decopperised anode slime is removed by oxidizing the same in the presence of sulphuric acid, thus leaving behind silver, gold and other metals. The anode slime stripped of selenium is charged to a furnace called TROF, to remove elemental impurities in the form of a slag known as Dore Slag. The dore slag mainly consists of gold and silver along with the presence of platinum and palladium group of metals in small traces.

[005] Normally, such dore slag is recycled back to copper smelter. However, recycling of dore slag to copper smelter is not advisable due to the presence of significant lead impurities in the dore slag. Further, transporting of dore slag to lead smelters to recover lead increases the risk of loss of precious metals such as gold.

[006] A number of methods are known in the art for recovery of precious metals from dore slag.

[007] US4404022A relates to a pyro-metallurgical method of treating dore slag which comprises the steps of grinding the slag, mixing the obtained pulp with water to form a slurry, adding a suitable collector to the slurry for selective flotation of precious metals, adding a suitable frother, aerating the slurry to produce a precious metals concentrate in the form of a froth on top of the slurry, and separating said concentrate from the remainder of the slurry.

[008] US20120067169A1 relates to a pyro-metallurgical method for recovering precious metals from source materials containing precious metals which involves leaching the source material in aqua regia to provide a treated solid residue and processing the treated residue to recover precious metals.

[009] Under such circumstances where the source material comprises of complex elemental impurities, hydrometallurgical process of recovering precious materials is more suitable than pyrometallurgical processes. Hydrometallurgical processes consist of leaching of metals from source materials into aqueous solutions, followed by separation and concentration of the targeted metals from other metals by techniques such as precipitation, ion-exchange and adsorption have been used. Among the hydrometallurgical process, adsorption and ion-exchange are suitable when the dore slag source comprises only low or trace concentration of precious metals.

[010] P. Cyganowsk et al., in Journal of Saudi Chemical Society (2017) 21, 741-750 published a research work on the recovery of gold from the aqua regia leachate of electronic parts using a core–shell type anion exchange resin. The article focuses on recovery of gold from electronic parts using anion exchange resin.

[011] Katsutoshi Inoue et al., relates to a Gold Recovery Process from Primary and Secondary Resources Using Bio adsorbents (DOI: 10.5772/intechopen.84770). Katsutoshi Inoue et al., provides bio adsorbents exhibiting high selectivity only to gold over other metals. By using these biosorbents, recovery of gold from actual samples of printed circuit boards of spent mobile phones and Mongolian gold ore was investigated.

[012] The composition of dore slag is shown in Table 1.

[013] Table 1: composition of dore slag, conventionally known
Component Wt %
Cu 0.4 - 2.5
Se 0.2 – 58
Te 0.02 - 0.4
Pb 3 – 50
As 0.05 – 0.2
Sb 0.1 – 3.2
Bi 0.1 – 0.5
Sn 0.2 - 0.8
Ag (%) 1 – 2
Au (ppm) 50-200

[014] As seen in table 1, the dore slag is a complex source of precious metal having a number of impurities. Hence, recovery of gold from dore slag as a source material is a challenge duo to complex elemental impurities and low amount of residual gold.

SUMMARY OF THE INVENTION

[015] It is an object of the present invention to obviate the above challenge by providing a method for recovering gold from dore slag.

[016] The present invention provides a process in which the natural affinity of gold as metal for a leachate is utilized to achieve separation of such gold from other particulate material.

[017] In an embodiment, the process for recovery of gold comprises of passing a mother liquor comprising gold through an adsorbent resin to absorb gold selectively and recovering the adsorbed gold from the resin.

[018] The process of the invention is a process for recovery of gold from dore slag, which comprises the steps of grinding the dore slag and leaching the grounded slag with an aqueous acidic solution to obtain a slurry. The slurry is then subjected to filtration to separate mother liquor and a filter cake. Subsequently the mother liquor is passed through an ion exchange column comprising an adsorbent. The adsorbent in ion exchange column has a selectivity towards gold in the mother liquor, thereby adsorbing residual gold in mother liquor.

[019] The gold-loaded adsorbents are incinerated leaving solid gold particles in the incineration residues. The incineration residues are further dissolved in an acidic solution and allowed to precipitate other impurities. The process further comprises of electrowining of gold particles impregnated with acidic solution for recovery of gold particles.

BRIEF DESCRIPTION OF THE DRAWINGS

[020] Figure 1 depicts the experimental setup of the process of the present invention.

[021] Figure 2 depicts gold leachability with respect to particle size by showing the effect of particle size of gold on dissolution in aqua regia for various grain size at 40°C and 200 rpm.

[022] Figure 3 depicts effect of temperature for recovery of gold at agitation speed of 200 rpm.

[023] Figure 4 depicts detailed process of the present invention.

DESCRIPTION OF THE INVENTION
[024] In describing and claiming the invention, the following terminology will be used in accordance with the definitions set forth below. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein. As used herein, each of the following terms has the meaning associated with it in this section. Specific and preferred values listed below for individual process parameters, substituents, and ranges are for illustration only; they do not exclude other defined values or other values falling within the preferred defined ranges.
[025] As used herein, the singular forms "a," "an," and "the" include plural reference unless the context clearly dictates otherwise.

[026] The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention

[027] As used herein, the terms “comprising” “including,” “having,” “containing,” “involving,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to.

[028] As used herein, the term “dore slag” refers to slags produced as byproducts during treatment of refinery slime in TROF in precious metal refinery in copper smelters. They generally contain lead and small amounts of silver, antimony, tellurium and other metals. Depending on the fluxing agent used, slags in this group may contain metal oxides, phosphates, silicates, sulphides/sulphates and/or fused salts in varying concentrations.

[029] As used herein, the term “electrolytic refining” refers to electrolytic refinery refers to the copper electrochemical refinery where copper anodes from copper smelter are electrochemically refined using electrolysis process.

[030] As used herein, the term “electrowining” also called electroextraction, is the electrodeposition of metal from acidic solution after leaching or electrolysis process.

[031] As used herein, the term “leaching” refers to the process by which constituents of a solid material are released into a contacting liquid phase. Leaching is usually done with a strong acid or strong base.

[032] As used herein, the term “leachate” refers to the liquid phased produced after filtration of leaching solution.

[033] Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described. All publications and other references mentioned herein are incorporated by reference in their entirety. Numeric ranges are inclusive of the numbers defining the range.

[034] It is well known that anode slimes from the electrolytic refining of copper are treated to remove therefrom as much copper, selenium and tellurium as possible and the remainder material is then smelted in the TROF to produce dore slag consisting essentially of silver, gold and other precious metals.

[035] Increasing demand for precious metals has led to development of various cost-effective processes of their refining, separation and purifications from dore slag. Adsorption using ion exchange resins is an efficient method for extraction of precious metals currently in industry. For the effective separation, adsorbent resins having high selectivity and high loading capacity for targeted precious metal is essential.

[036] The present invention will now be further described with reference to the figure appended hereto and representing a flow sheet of the method according to a preferred embodiment of this invention.

[037] In an embodiment, the present invention relates to a process for recovery of gold by passing a mother liquor comprising gold through an adsorbent resin to adsorb gold selectively, wherein the resin is macroporous polystyrenic based chelating resin having thiouronium group and recovering the adsorbed gold from the resin.

[038] The mother liquor is obtained by leaching dore slag comprising gold with an acidic solution at a temperature in a range of 80°C to 120°C for 2 hours to 4 hours under atmospheric pressure to obtain a slurry and subjecting the slurry to filtration to separate mother liquor comprising gold and a filter cake.

[039] The adsorbed gold from the resin is recovered by subjecting the resin having adsorbed gold to incineration to obtain a black residue comprising gold followed by dissolving the black residue comprising gold in an acidic solution and electrowinning the solution to obtain gold particles.

[040] Referring to figures 1 and 4, the dore slag from TROF is grounded to reduce the size of dore slag. In an embodiment, grinding of dore slag is carried out in laboratory ball mill. The grinding of dore slag is done to ensure superior leaching by maintaining higher contact between solid and leachant of particle size <150 micrometer. The dore slag is grinded to a pre-determined fitness of 50 microns to 100 microns. The concentration of gold in grinded dore slag is 50 ppm to 200 ppm.

[041] The grounded dore slag particles are placed in a dore slag leaching unit, typically a glass beaker (~500 ml) The dore slag are subsequently mixed with an aqueous acid solution to form a slurry of grounded slag particles. The aqueous acidic acid is an oxidizing mixture capable of leaching the dore slag and with a particular affinity towards gold. The leaching of dore slag by the aqueous acidic solution dissolves the elemental gold in the dore slag.

[042] In an embodiment, the leaching is carried out at a temperature in the range of 80 oC to 120oC while maintaining a constant stirring of the slurry. The temperature of leaching is maintained by heating the glass beaker facilitated by a hot plate under the flume hood. A PID (Proportional, Integral and Derivative) digital program temperature controller integrated with the thermocouple was built onto the hot plate. The duration of stirring is in the range of 2 hours to 4 hours. The amount of dore slag leached is in a range of 95% to 99%.

[043] In an embodiment, the aqueous acidic solution is aqua regia, comprising a mixture of nitric acid and hydrochloric acid, optimally in a molar ratio of 1:3. (aqua regia is a specific acid which is formed only when the ratio of HNO3: HCl is 1:3).

[044] The ratio of aqua regia to dore slag is in the range of 8 to 10. The leaching is extremely low at the lower end of the aqua regia as the dore slag is extremely stable. The dore slag is produced from the TROF (Tilting Rotating Oxy-Furnace) where temperature range is 800°C to 1200 °C which makes the slag extremely stable, and it is very difficult to leach out gold.

[045] The chemical reactions occurred during this process are represented below:

(1)
(2)
(3)
(4)

[046] The leached slurry is then filtered to separate mother liquor, also known as leachate and a filter cake. The mother liquor comprises of the metal impurities from the dore slag dissolved therein. Preferably the filtration is carried out in vacuum using a filter paper having mesh size of 40 and 41.

[047] In an embodiment, the mother liquor is chemically treated with urea for de nitrification of the mother liquid to remove residual to remove residual nitric acid from the mother liquor. Subsequently the urea treated mother liquor is passed through an ion exchange column comprising an adsorbent bed. The adsorbent bed in ion exchange column has a selectivity towards gold in the mother liquor, thereby adsorbing residual gold in mother liquor. In an embodiment, the adsorbent bed comprises of synthetic resins, selected from a group consisting of macroporous polystyrenic based chelating resin, with thiouronium group. The adsorbent bed is preferably, Purolite S920. In an embodiment, the duration of contact of urea treated mother liquor with the resin bed formed in a glass column. The flow rate maintained was 30-30 ml per min. The contact time of the mother liquor and the resin is 60 minutes to 90 minutes. The amount of gold adsorbed is 40 gram per liter to 50 gram per liter on the resin. The adsorption efficiency of gold is in a range of 94% to 99%. The feed inlet sample and outlet samples were sent for gold analysis in Atomic Adsorption Spectrophotometry (AAS).

[048] The gold-loaded adsorbents are subjected to incineration, thereby leaving gold particles in the incineration residues. Incineration of gold loaded adsorbents is carried out in in a furnace setup at a temperature in the range of 500°C to 700 °C. The incineration of adsorbents comprising gold results in black residue. The black residue contains 1000 ppm to 1500 ppm gold. The residue left after filtration of leachate solution was dried and pulverized and sent for analysis in Atomic Adsorption Spectrophotometry (AAS).

[049] The incineration residues, free of resins, are further mixed in an acidic solution, thereby allowing the gold particles to be dissolved in the acidic solution. Any other metal impurities are precipitated. The acidic solution is the aqueous acidic solution is aqua regia, comprising a mixture of nitric acid and hydrochloric acid, optimally in a molar ratio of 1:3. The ratio of aqua regia to urea is 3:9:1.

[050] The process further comprises of electrowining of gold particles impregnated acidic solution for recovery of gold particles. Electrowining of gold particles is carried through a Wohlwill process wherein the crystals are separated out to case the metal (gold) in biscuits or plates.

[051] The process of the present invention can be used to recover gold particles having size in the range of 100 micrometers to 150 micrometers from dore slag. The total amount of gold recovery is in a range from 88% to 95%. Further, the present process does not require a high capital cost plant to operate it, and the energy demand is also optimal, thereby reducing operating costs. Environmental problems associated with the process of the present invention are low since it avoids the use of highly toxic materials.

[052] Thus, the stepwise process is as follows:
[053] Step 1: Sample preparation: the dore slag sample was finely grounded.
[054] Step 2: Leaching and filtration: dore slag (which had a lean concentration of Au was leached in an acid solution. The leaching step was targeted for maximum transfer of gold in the acid. After leaching the solution was filtered for separation of mother liquor and cake (mainly impurities).
[055] Step 3: Adsorption: the mother liquor (leached solution) was passed through the resin bed which preferentially absorbed gold.
[056] Step 4: Incineration: the exhausted organic resin was incinerated (to break bond formation between resin and Au) and remaining solid recovered was majorly gold.
[057] Step 5: Dissolution and precipitation: the remaining solids were again dissolved in the acidic solution. The solution had higher concentration of Au with no impurities. Precipitation step was followed same as it was followed in PMR Plant.
[058] Step 6: Electrowinning: the solution was ready for the recovery of gold and PGMs as metal in Wohwill cells. Crystals were then separated out to cast the metal in biscuits or plates.

[059] The invention will now be described with reference to the following examples. It is to be understood that the examples are provided by way of illustration of the invention and that they are in no way limiting to the scope of the invention.

[060] WORKING EXAMPLES

[061] Example 1: Leaching of dore slag

[062] 30 gm dore slag comprising 156 ppm of gold concentration was leached in the presence of 120 ml and 300 ml aqua regia (acidic solution) at various temperatures and time periods to obtain a slurry. The hot slurry was cooled down for few hours in order to allow particle settling which resulted in leachate solution. This solution was then filtered through vacuum filter paper of mesh size 40 and 41. Filtered leachate solution was further analyzed.

[063] Samples 1 and 2 represents comparative example, wherein the dore slag was leached only for 0.5 hours and 1.5 hours. Samples 3 to 5 represents present invention examples, wherein the dore slag was leached for a time period in a range of 2 to 4 hours.

[064] The process parameters and results for comparative samples 1 to 5 is given below in Table 2.

[065] Table 2: Process parameters and results of leaching gold

Comparative
Sample 1 Comparative
Sample 2 Sample 3 Sample 4 Sample 5
Amount of Dore slag (gm) 30 30 30 30 30
Concentration of gold
(ppm) 156 156 156 156 156
Amount of Aqua regia (ml) 120 300 300 300 300
Solid/ liquid ratio 0.25 0.1 0.1 0.1 0.1
Temperature 90°C 105°C 105°C 105°C 105°C
Time
(hours) 0.5 1.5 2 2.5 3
Results
Amount of dore slag leached
(ml) 240 245 240 260 235
Concentration of gold
(ppm) 12.52 13.38 18. 55 17.62 19.8
Leaching % 64.21% 70.05% 95.13% 97.88% 99.30%

[066] From the above table, it can be concluded that when dore slag of Samples 4 to 6 was leached at a temperature of 105°C for a time period of 2 hours to 4 hours wherein the ratio of aqua regia to dore slag is 1:10, then the amount of gold leached was 94% to 99% whereas when dore slag of Comparative Sample 1 was leached at 90°C for 0.5 hours wherein the ratio of aqua regia to dore slag was 1:4, then the amount of gold leached was only 64.21% and when dore slag of Comparative Sample 3 was leached at temperature 105°C but for 1.5 hours only with ratio of aqua regia to dore slag as 1:10, then the amount of gold leached was only 70.05%.

[067] Example 2: Adsorption and recovery of gold

[068] Sample 5 of Table 2, as explained above, was further subjected to adsorption and recovery of the gold which is explained in below table 3.

[069] The filtered leachate solution of Sample 5 was then treated with neutralizing agent, that is, with urea to remove residual HNO3 from the solution and then the solution was passed through an ion exchange resin bed.

[070] Ion exchange column selectively adsorbed gold in the solution. The adsorbent resin was macroporous polystyrenic based chelating resin having thiouronium group. i.e., Purolite S920.

[071] The resin comprising gold was incinerated. The temperature of incineration was 600°C. The incineration of adsorbents comprising gold results in black residue. The residue left after filtration of leachate solution was dried and pulverized and sent for analysis in Atomic Adsorption Spectrophotometry (AAS).

[072] The black residue was further mixed with an acidic solution, thereby allowing the gold particles to be dissolved in the acidic solution. Any other metal impurities were precipitated. The acidic solution was the aqueous acidic solution is aqua regia, comprising a mixture of nitric acid and hydrochloric acid, optimally in a molar ratio of 1:3. The ratio of aqua regia to urea is 3:9:1.

[073] The resultant solution was sent for electrowining of gold particles impregnated in acidic solution for recovery of gold particles. Electrowining of gold particles was carried through a Wohlwill process wherein the crystals were separated out to case the metal (gold) in biscuits or plates.

Total recovery of gold was calculated as follows:

[074] Results of the adsorption and recovery of gold is represented in Table 3 below:

[075] Table 3: Process parameters and results for recovery of gold:
Sample 6 Sample 7
Amount of dore slag 30 gm 30 gm
Concentration of gold in dore slag 156 ppm 156 ppm
Mass of gold in dore slag 4.68 mg 4.68 mg
Amount of aqua regia 300 ml 300 ml
Solid/liquid ratio 0.1 0.1
Temperature 105°C 105°C
Time 3 hours 3 hours
Amount of dore slag leached (leachate) 250 ml 275 ml
Concentration of gold in leached dore slag (leachate) 17.2 ppm 16.65 ppm
Mass of gold in leached dore slag (leachate) 4.45 mg 4.51 mg
Leaching % 95.05% 96.5%
Amount of residue after leaching 17.45 gm 15.1 gm
Concentration of gold in residue after leaching 6.5 ppm 10.6 ppm
Mass of gold in residue after leaching 0.101 mg 0.160 mg
Volume of final effluent after adsorption 220 ml 245 ml
Concentration of gold in final effluent after adsorption 0.8 ppm 1.06 ppm
Mass of gold in final effluent after adsorption 0.176 mg 0.259 mg
% Adsorption of gold 96.16% 94.24%
Mass of black residue after incineration 3.68 gm 3.01 gm
Concentration of gold in black residue after incineration 1210 ppm 1395 ppm
Mass of gold in black residue after incineration 4.45 mg 4.198 mg
Total gold recovery
(Fire assay) 95.15% 89.72%

[076] From the above table, it can be concluded that both the samples 6 and 7, leached higher amount of gold, adsorbed higher amount of gold and therefore, recovered higher amount of gold.

[077] EXAMPLE 3: Experimental parameters for gold leaching, adsorption and recovery
[078] The primary dore slag samples received from precious metal recovery plant were crushed to finer size and powder was characterized by particle size distribution. The elemental analysis was carried out fire assay and XRF (X-ray fluorescence). Leaching studies were carried out aqua regia solution (a mixture of nitric acid and hydrochloric acid in 1:3) using various concentrations and other variables like temperature, reaction time etc.

[079] Gold was recovered from primary dore slag; the primary dore slag was received from precious metal recovery plant from copper smelter. The process involves sizing of primary dore sag, selective leaching of gold from dore slag using aqua regia solution (a mixture of nitric acid and hydrochloric acid in 1:3). Followed by pre-treatment of mother liquor through ultra- filtration and passing through resin bed for selective adsorption of gold particles. Further, this resin was incinerated to get gold rich powder which is recycled back into slime smelting furnace for gold recovery as pure metal. Effluent stream and residue produced during process were characterized.

Table 4: Experimental Parameters
Dore Slag (concentration of gold was 156 ppm) 30 gram
Temperature 90 °C to 105 °C
HNO3 75 ml
HCl 225 ml
Urea 20 gm
No. of re-circulations 1- 2
Ion Exchange Bed Purolite S920 Resin

[080] All the parameters given in below table were based on 30/300 g of primary dore slag powder.

[081] Figure 2 represents effect of particle size on gold dissolution in aqua regia for various grain size at 40°C and 200 rpm. Leachability with respect to particle size was studied, results of gold leachability and particle size are presented in Figure 2.

[082] Figure 3 represents effect of temperature for recovery of gold at agitation speed of 200 rpm.

[083] Based on the studies conducted above from Figures 2 and 3, results are disclosed in Table 5 which represents the major parameter to be controlled during leaching step are powder size, solid-liquid ratio in reactor, concentration of leachant, reaction time and temperature. For gold adsorption resident time, resin adsorption capacity etc.

[084] Table 5: Optimum Conditions for Selective Au Leaching and Resin Adsorption
Gold Leaching Gold Adsorption
Particle size <10 micron Resin Purolite S920
Temperature 90 °C to 105 °C number of pass 2
Solid/Liquid ratio 20% Reaction time 60 minutes to 90 minutes
HNO3 : HCl: Urea 3:9:1 Au adsorption 45 g/lit
Reaction time 2 hours to 3 hours
% Au Leachability 95% to 99% % Au Adsorption 94% to 96%

[085] Another key factor to be considered was reaction time for leachability as selective gold leaching. And temperature for leaching to be maintained between 90°C to 100°C.

[086] Example 4: efficiency of gold leaching, adsorption and recovery

[087] Sample 8 according to the present invention was prepared as follows:
[088] 50gm of dore slag from TROF was taken and grounded in laboratory ball mill to reduce the size of dore slag in the range of 50 micron to 100 micron. The grounded dore slag was mixed with 500 ml of aqua regia in a 1000ml beaker thereby allowing leaching of dore slag by aqua regia. The mixture was heated using a hot plate to a temperature of 105°C while maintaining constantly stirring for 2.5 hours. The leaching of dore slag by the aqueous acidic solution dissolved the elemental gold in the dore slag.

[089] The leached dore slag was then filtered to separate mother liquor leachate and a filter cake. The mother liquor comprises of the metal impurities from the dore slag dissolved therein. The filtration was carried out in vacuum using a filter paper having mesh size of 40 and 41. Subsequently the filtered mother liquor was treated with urea to remove any residual nitric acid from the mother liquor. Subsequently the urea treated mother liquor was passed through an ion exchange column with 35 ml resin. The resin used was macroporous polystyrenic based chelating resin, with thiouronium group, Purolite S920. The resins in ion exchange column had a selectivity towards gold in the mother liquor and adsorbed residual gold in mother liquor.

[090] The gold-loaded adsorbents were incinerated in a heating furnace at a temperature 500 °C to 700 °C. The residual gold particles adsorbed on to the resins were separated as residue along with other impurities by incineration. The incineration residues, free of resins, were recycled back in TROF for gold recovery.

[091] The efficiency of gold leaching, efficiency of gold adsorption and the efficacy of gold recovery is calculated by the following parameters.

% gold leaching efficiency (eleach) = [(Auleachate* V)/ (1000000 * MAu_feed)]*100
% gold Adsorption efficiency (eadsorb) = [1- (Aueffluent /Auleachate)] *100
% total gold recovery (€) = eleach * eadsorb

Where
Auleachate = concentration of gold in leachate (ppm)
Aueffluent = concentration of gold in effluent (ppm)
MAu_feed = mass of gold in dore slag in (gm)
V = Volume of leachate (ml)
[092] The data in table 6 shows the efficacy and percentage of gold recovery from dore slag using the process described herein.

[093] Table 6: Results of Sample 8 for gold leaching, adsorption and recovery efficiency:
Dore Slag (Au ppm) Concentration of gold in incinerated residue (Au ppm) Final Effluent (Au ppm) Au Leaching Efficiency
eleach Au Adsorption Efficiency eadsorb % Au recovery
eleach* eadsorb

100-200 1200 ppm to 1500 ppm 5-10 >95% 97%-99% >95%

[094] The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to a person skilled in the art, the invention should be construed to include everything within the scope of the disclosure
,CLAIMS:

1. A process for recovery of gold, the process comprising:
(a) passing a mother liquor comprising gold through an adsorbent resin to adsorb gold selectively, wherein the resin is macroporous polystyrenic based chelating resin having thiouronium group; and
(b) recovering the adsorbed gold from the resin.

2. The process as claimed in claim 1, wherein the amount of gold adsorbed is 40 gram per liter to 50 gram per liter on the resin.

3. The process as claimed in claim 1, wherein, the contact time of the mother liquor and resin is 60 minutes to 90 minutes.

4. The process as claimed in claim 1, wherein, the gold adsorption efficiency is in a range of 94% to 99%.

5. The process as claimed in claim 1, comprising recovering the adsorbed gold from the resin by
(a) subjecting the resin having adsorbed gold to incineration to obtain a black residue comprising gold;
(b) dissolving the black residue comprising gold in an acidic solution; and
(c) electrowinning the solution to obtain gold particles.

6. The process as claimed in claim 5, wherein the incineration is carried out at a temperature in a range of 500°C to 700°C.

7. The process as claimed in claim 5, wherein, the black residue contains 1000 ppm to 1500 ppm gold.
8. The process as claimed in claim 1, comprising obtaining the mother liquor by
(a) leaching dore slag comprising gold with an acidic solution at a temperature in a range of 80°C to 120°C for 2 hours to 4 hours under atmospheric pressure to obtain a slurry; and
(b) subjecting the slurry to filtration to separate mother liquor comprising gold and a filter cake.

9. The process as claimed in claim 8, wherein the dore slag is produced from Tilting Rotating Oxy-furnace (TROF) at 800°C to 1200°C in precious metal recovery plant.

10. The process as claimed in claim 9, wherein the dore slag is grinded to pre-determined fitness of 50 micron to 100 micron.

11. The process as claimed in claim 10, wherein concertation of gold in grinded dore slag is 50 ppm to 200 ppm.

12. The process as claimed in any one of the preceding claims, wherein the acidic solution is aqua regia comprising a mixture of nitric acid and hydrochloric acid in a molar ratio of 1:3.

13. The process as claimed in claim 8, wherein the ratio of acidic solution to the dore slag is in a range of 8 to 10.

14. The process as claimed in claim 8, wherein the amount of gold leached is in the range of 95% to 99%.

15. The process as claimed in claim 1, comprising optionally treating the mother liquor with urea before passing the mother liquor through the resin.
16. The process as claimed in claim 15, wherein the ratio of aqua regia to urea (HNO3: HCl: Urea) is 3:9:1.

17. A process for extraction and recovery of gold from dore slag, the process comprising steps of:
(a) acid leaching the dore slag at a predetermined temperature and duration under atmospheric pressure;
(b) passing mother liquor comprising gold of step (a) through an adsorbent resin to adsorb gold selectively;
(c) incineration of gold adsorbed resin from step (b) to produce gold rich black residue;
(d) dissolving the gold rich black residue of step (c) in an acidic solution; and
(e) electrowinning the solution of step (d) to obtain gold as powder particles.

18. The process for extraction and recovery of gold as claimed in claim 17, wherein the dore slag comprising gold is grinded before acid leaching.

19. The process as claimed in any one of the preceding claims, wherein the total amount of gold recovered is in a range of 88% to 95%.