Description:FIELD OF THE INVENTION
[001] The present disclosure relates to a process of recovering metal from a smelter slag. The disclosure particularly relates to the process of recovery of zinc and lead from a smelter slag by slow cooling, sulphidization and froth flotation.

BACKGROUND OF THE INVENTION
[002] During the processing of lead-concentrate through Ausmelt furnace, apart from producing lead bullions of >99% purity, the waste product (lead smelter slag) is also generated which contains various valuable elements especially lead (Pb) and zinc (Zn), in the form of oxides, silicates, sulphates and complex minerals.

[003] Reference may be made to J.E. Dutrizac et.al, [Method for processing siliceous zinc ores, Lead-Zinc, 2000] and Abkosh et al, [Review of the Hydrometallurgical Processing of Non-Sulfide Zinc Ores, Hydrometallurgy (2014)], wherein oxide materials are easily treated by routes such as leaching. Here the disadvantage is leaching of silicate, which is complicated due to the dissolution of silica causing gelation and demands solvent extraction to build zinc concentration for subsequent electrowinning.

[004] Reference may also be made to Hay et al., [Miner. Eng., 1994,], wherein commercially available process to recover metals from the slags and other wastes is slag fuming such as in rotary kiln in which reduction is carried out using large quantity of coal, coke or other reducing agents and air at above 1200°C. Reduced zinc and lead are volatilized from the slag and may be re-oxidized to metal oxides in the outlet gas stream and collected as dust, thereafter, recovered by acid leaching or other processes. The drawbacks with slag fuming are high energy consumption, low recovery of metals and metallic fumes like Pb, Cd and as produced during the process are high risk to peoples’ health.

[005] Reference may be made to CN201310065266, wherein dressing-smelting combined treatment method for sulfate-containing lead-zinc smelting slags to obtain zinc and lead concentrate. The method comprises the following steps: 1) drying: carrying out heating and drying treatment on slag charges; 2) roasting: adding a reducing agent into the dried slag charges so as to carry out reduction roasting; 3) after the roasting is completed, slowly cooling the slag charges, and after the temperature of the slag changes is reduced to below 200 ̊C, carrying out water quenching on the slag charges so as to obtain water-quenched slags; and 4) grinding and flotation: after the water-quenched slags are subjected to ore grinding and grading, taking a material with the particle size of less than 75 µm and carrying out flotation separation on the material so as to obtain a lead concentrate and a zinc concentrate. The drawbacks with (reduction) roasting is high energy and carbon consumption.

[006] Hence, there is need for development of green alternative process for the recovery of lead and zinc from the smelter slag, which works on low energy consumption, and do not emit toxic metallic fumes.

OBJECTS OF THE INVENTION:
[007] Some of the objective of the present disclosure, with at least one embodiment herein satisfy, are listed herein below:

[008] A primary objective of the present disclosure is to provide a green alternative process for obtaining lead and zinc concentrates from smelter slag.

[009] Another objective of the present disclosure is to provide a process to separate zinc and lead from the lead and zinc smelter slag, where the process is cost-effective.

[010] Another objective of the present disclosure is to provide a beneficiation process to improve the content of lead and zinc in concentrates obtained from the lead smelter slag.

[011] Yet another objective of the present disclosure is to provide lead and zinc concentrate from the smelter slag with higher recovery rate.

SUMMARY OF THE INVENTION
[012] The present disclosure relates to a process for obtaining lead and zinc concentrates from smelter slag comprising the steps of draining a slag directly from the smelter and cooling the drained slag naturally in air; grinding and sulfidizing the cooled slag; and froth floating the sulphidized slag to obtain the lead and/or zinc concentrate.

BRIEF DESCRIPTION OF THE DRAWINGS
[013] The disclosure may be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows:

Figure 1 depicts (a) Scanning Electron Microscope-Back Scattered Imaging (SEM-BSI) of fast cooled lead smelter slag; (b) SEM-BSE of slow cooled lead smelter slag and (c) Minerology Analysis of slow cooled lead smelter slag

Figure 2 depicts phase separated slow cooled lead smelter slag post grinding (P80: 63 microns)

Figure 3 depicts the effect of sulphidization condition prior to flotation on (a) flotation nature of Willemite and Hardystonite & (b) Recovery (flotation) of Pb and Zn (c) Effect of additives on recovery of Pb and Zn

Figure 4 depicts the effect of variation of collector on (a) Recovery of Zn and Pb and mass pull (b) Grade of Zinc and Lead in the flotation concentrate.

Figure 5 depicts the effect of ZnSO4 under variable sulphidation condition on (a) variation of lead grade in the concentrate and (b) The floatation behaviour of Willemite and Hardystonite.

Figure 6 depicts double stage flotation technique with variation of sulphidizing agents on recovery of lead and Zinc
DETAILED DESCRIPTION OF THE INVENTION
[014] The detailed description of various exemplary embodiments of the disclosure is described herein. It should be noted that the embodiments are described herein in such details as to communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure.

[015] It is also to be understood that various substitutions/arrangements/permutations or combinations may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, intended to encompass equivalents thereof.

[016] The terminology used herein is to describe particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context indicates otherwise. It will be further understood that the terms “comprise”, “comprising”, “includes” and/or “including” when used herein, specify the presence of stated features, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components and/or groups thereof.

[017] As used herein, the words “preferred” and “preferably” refer to embodiments of the technology that 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 technology.

[018] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[019] Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present technology. The appearance of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but no other embodiments.

[020] The term “smelter slag” in the context of the present disclosure defines a waste material or impurities remained after smelting a metal from its ore. In one of the embodiments of the present disclosure, the smelter slag may be a lead and/or zinc smelter slag.

[021] The term “froth-flotation” in the context of the present disclosure defines a physicochemical process that separates particles based on differences in surface wettability. For
Example, froth flotation of smelter slags can produce concentrates of minerals of zinc, and lead. The froth-flotation process may include single step flotation or double stage flotation.

[022] The term “slow cooling” in the context of the present disclosure defines draining the molten slag obtained from the smelter and cooling it naturally at ambient temperature. The ambient temperature is defined as temperature in the range of 10 to 500C.

[023] The term “and/or” in the present disclosure includes the embodiments, where the two components are either used together to achieve the objective of the present disclosure or any one is used to achieve the objective of the present disclosure. The said term includes the scope of both the embodiments.

[024] The present disclosure provides a process of separating metal concentrate from the smelter slag. In particular, the present disclosure relates to the process of separating metal concentrate from smelter slag comprising the steps of: draining a slag from a smelter and cooling the drained slag; grinding and sulfidizing the cooled slag; and froth floating the sulphidized slag to obtain the metal concentrate.

[025] In an embodiment of the present disclosure, the process of separating at least one of lead and zinc concentrate from smelter slag comprising the steps of: draining a slag directly from the smelter and cooling the drained slag naturally in air; grinding and sulfidizing the cooled slag; and froth floating the sulphidized slag to obtain the lead and/or zinc concentrate.

[026] In an embodiment of the present disclosure, the slag is obtained from an Ausmelt furnace operating with lead-concentrate as feed.

[027] In an embodiment of the present disclosure, the smelter slag comprises Hardystonite (Ca2ZnSi2O7), Willemite (Zn2SiO4), Zinc Oxide (ZnO), Iron oxide (FeO), Melilite, Lead oxide (PbO), Zinc sulphide (ZnS), and lead sulphide (PbS).

[028] In an embodiment of the present disclosure, the cooling the drained slag comprises slow cooling of the drained slag that allows the phase separation of the slag into minerals. The slow cooling is then followed by wet grinding for liberating the minerals. The slow cooling is carried out naturally in the air at an ambient temperature. The ambient temperature is defined in the range of 10 to 500C

[029] In an embodiment of the present disclosure, the beneficiation process is employed to enhance the recovery rate of the metal concentrate. In particular, the beneficiation process has helped in producing concentrates rich in zinc and / or lead. One of the processes for beneficiation is the flotation, which has not been yet employed for lead smelter slag as flotation feed. The present disclosure uses the froth flotation process as a beneficiation process, which is required for the formation of separate phases of the minerals, to allow use of collector to render the particles with different hydrophobicity. Such separation of phases may require the slag to be treated at appropriate conditions especially at ambient temperature and time.

[030] In an embodiment of the present disclosure, the flotation process is considered to be the cheapest and best process available for recovering zinc and lead from their ores. However, the reason of not employing this process in recovering zinc and lead from smelter slag is that slag is normally water-quenched that hinders the phase-separation, and hence hinders mineral liberation from each other during grinding. Further, flotation of oxide components is difficult compared to sulfide ores. In order to float zinc oxide and silicates minerals using different reagents, pre-sulfidation is necessary.

[031] In an embodiment of the present disclosure, sulfidization step on the slow-cooled slag is carried out before the flotation step by using sulfidizing agent.

[032] In an embodiment of the present disclosure, the process includes grinding and sulfidizing of the cooled slag, The grinding and sulfidizing step comprises co-grinding the cooled slag with a sulfidizing agent. In an embodiment, the co-grinding the slag with sulfidizing agent converts ZnO to ZnS by a process called mechano-chemical processing. In embodiments, the co-grinding of the cooled slag with a sulfidizing agent occurs in ball mill. During ball powder collisions, repeated fractures continually regenerate new interfaces which results in sulphidation reactions at low temperatures which otherwise would normally have occurred at high temperatures. Due to the solid-state reactions induced by mechanical forces, formation of ZnS and PbS takes place without releasing hazardous gases. This is without additional high temperature and energy consuming heating where sulfidization is achieved by high temperature reactions of oxides with iron or sodium sulfides.

[033] In another embodiment of the present disclosure, the grinding and sulfidizing the cooled slag comprises grinding the cooled slag followed by sulfidizing the grounded slag with the sulfidizing agent. In one of an embodiment of the present disclosure, the grinding of the cooled slag occurs in ball mill. The grounded and sulfidized slag has particle size in the size range of 30 to 200 microns. In preferred embodiment P80 of the grounded and sulfidized slag is 63 microns. The term “P80” in the context of the present disclosure defines that 80% of grounded particles pass through the particular screen size. However, the said particle size is not at all limiting in nature but is mentioned as an exemplary size. The particle size of grounded and sulfidized slag includes all the optimization/variation that can be passed through the screen size.

[034] In an embodiment of the present disclosure, grinding and sulfidizing the cooled slag comprises either co-grinding the cooled slag with a sulfidizing agent or grinding the cooled slag followed by sulfidizing the grounded slag with the sulfidizing agent without employing substantial heating.

[035] In an embodiment of the present disclosure, the sulfidizing agent is selected from the group consisting of sodium sulfide (Na2S), elemental sulfur, ammonium sulphide ((NH4)2S), sodium hydrogen sulphide (NaSH), calcium sulphide (CaSx), and a combination thereof. Preferably, the sulifidizing is Na2S or elemental sulphur. The sulfidizing agents are not limited to the examples given here but also include those sulfidizing agents having similar characteristics as those of the above-mentioned sulfidizing agents.

[036] It is observed that the dissociation of sodium sulfide will give HS-, which gets observed on the surface of the silicate mineral. Na2S react with water to produce H2S, which will further dissociate into H+ and OH-. Sodium sulfide makes the silicate surface more negative and favours the electrostatic attraction mechanism between amines and the silicate surface. The collectors such as amines used during flotation step seem to be effective for silicate ores, when used after sulfidation.

[037] In an embodiment of the present disclosure, the froth flotation is carried out in single stage circuit. In another embodiment, the froth flotation is carried out in double-stage circuits. In embodiment, the froth flotation comprising adding iron and zinc depressant, carbon depressant, lead and zinc promoter, zinc activator, collector, and frother.

[038] In an embodiment of the present disclosure, the frother is selected from the group consisting of pine oil, methyl isobutyl carbinol (MIBC), and a combination thereof. The frother is not limited to the examples given here but also include those frothers having similar characteristics as those of the above mentioned frother.

[039] In an embodiment of the present disclosure, the collector is selected from the group consisting of potassium amyl xanthate (PAX), sodium isopropyl xanthate (SiPX), Octadecyl amine, sodium ethyl xanthate, sodium isobutyl xanthate, potassium ethyl xanthate, and a combination thereof. The collectors are not limited to the examples given here but also include those collectors having similar characteristics as those of the above-mentioned collectors. In general, the purpose of the collector is to select form a hydrophobic layer on a given mineral surface in the flotation pulp and thus provide conditions for attachment of the hydrophobic particles to air bubbles and recovery of such particles in the froth product

[040] In an embodiment of the present disclosure, the lead and zinc promoter is selected from the group consisting of dithiophosphate (DTP), monothiophosphate, thionocarbamate, dithiophosphinate, and a combination thereof. The lead and zinc promoter are not limited to the examples given here but also include those promoters having similar characteristics as those of the above mentioned promoters.

[041] In an embodiment of the present disclosure, the zinc depressant is zinc sulphate (ZnSO4).The zinc depressant are not limited to the examples given here but also include those promoters having similar characteristics as those of the above mentioned zinc depressants.

[042] In an embodiment of the present disclosure, the iron (Fe) depressant is selected from sodium cyanide (NaCN) or Na-metabisulfite. Iron depressants are added to supress Fe flotation that may reduce zinc and lead grade. The iron depressant are not limited to the examples given here but also include those promoters having similar characteristics as those of the above mentioned iron depressants.

[043] In an embodiment of the present disclosure, the zinc activator is copper sulphate (CuSO4). The zinc activator are not limited to the examples given here but also include those zinc activator having similar characteristics as those of the above mentioned zinc activators.

[044] The present disclosure also relates to a separated zinc and lead concentrate from the smelter slag in high recovery rate.

Examples:
[045] The disclosure will now be illustrated with working examples, which is intended to illustrate the working of disclosure and not intended to take restrictively to imply any limitations on the scope of the present disclosure.

[046] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs.

[047] Although methods and materials similar or equivalent to those described herein can be used in the practice of the disclosed methods and compositions, the exemplary methods, devices and materials are described herein. It is to be understood that this disclosure is not limited to particular methods, and experimental conditions described, as such methods and conditions may apply.

Example 1:
[048] The lead smelter slag produced from the Ausmelt furnace from Chanderiya plant in Udaipur, Rajasthan contains about 20% zinc along with 3-4% lead as confirmed by Atomic Absorption Spectrophotometer (AAS) (table 1). Lead smelter slag obtained from smelter was cooled by water jet quenching to make pellets (fast cooling) in accordance with the process generally used in the prior arts. To achieve the primary objective of the present disclosure, the molten slag obtained from the smelter was drained into slag pots and allowed to cool naturally at 30°C (slow cooling). The lead smelter slag obtained via fast cooling process and the slow cooling process were subjected to minerology studies.

[049] The slow cooled slag was jaw crushed to 2mm size and further grinded with sulfidizing agents (e.g. elemental sulphur and sodium sulphide (Na2S)) in ball mill upto a size having a P80 of 63 μm. The ground slag was characterized under Field emission scanning electron microscopy (FESEM) produced by Carl Zeiss (Sigma 300) with the Bruker EDS (XFlash 6160) for understanding the morphology and the phase identification using the mineralogy software made by Zeiss (Mineralogic).

[050] Post characterization, the grounded lead smelter slag was subjected to flotation testing in 1.25 litre capacity Outokumpu cell. The density of mixture of water and lead smelter slag was kept at around 1.3 gm/cc and the tests were performed at room temperature under standard atmospheric condition. Various types of reagents (frothers, collectors, promoters, depressants and conditioners) were added in different combination and concentrations to get the maximum recovery and grade of precious elements of the slag like zinc, lead, etc. Post flotation the concentrates were dried at a temp of 100- 150°C over a time span of 12-16 hrs. Double stage flotation having different circuits to separate Pb concentrate and Zn concentrate flotation was performed by adding respective depressants, frothers, collectors and promoters.In the first stage of flotation Zinc sulfate and PAX were used. In second stage, CuSO4, Octa and PAX were used.

Results and Discussions
[051] Figure 1 shows the results of minerology studies of the cooled lead smelter slag obtained via fast cooling process and slow cooling process.

[052] Fast cooled lead smelter slag was homogeneous and no phase separation was observed as shown in Figure 1(a). The slow cooled lead smelter slag showed four different phases based on composition, two light grey, one dark grey and one white phase. Bright white phases were abundant and have grain size in the order of 5-20 μm as shown in Figure 1 (b) SEM-BSE image. There was interlocking texture between zinc rich silicates with low zinc bearing silicate. These phases were occurring in the order of 100-300 μm. The elemental analysis and minerology classifications are shown in Table 1 and 2.
Table 1: Elemental Analysis of lead smelter slag
Elements Al Ca Fe Mg Mn Pb Zn Si O Trace Elements
Weight % 2.7 8.1 1.4 1 1 4.5 22 17 39 3-4

Table 2: Mineralogy Assay of slow cooled lead smelter slag
Mineral Phases Willemite Hardystonite Zincite Lead Oxide Iron Oxide Others
Weight % 32 44 11 3 6 4

[053] The chemical analysis of the slag as received by AAS showed that slag contains about 22% zinc and 4-5% lead. Minerology using FESEM (Fig 1 (c)) showed the presence of Hardystonite (Ca2ZnSi2O7), Willemite (Zn2SiO4), Zinc Oxide (ZnO), Iron oxide (FeO), Melilite, Lead oxide (PbO) in the slow cooled slag. Hardystonite contributes high weight percentage of the slag but has low zinc (4.5%) compared to willemite which contains 12.2% out of 20% of the zinc.

[054] The slow cooled lead smelter slag was grinded in the ball mill so that the P80 is 63 microns. Post grinding the minerology study was again conducted which showed that the different minerals are liberated mostly as shown in figure 2.

[055] The phase separated lead smelter slag was then subjected to flotation study and various parameters were analyzed to understand their effect on floatation of various minerals notably:

Effect of prior sulphidation:
[056] In lead smelter slag, the lead was present in the form of oxide and Zinc was present in the form of both oxide and silicates. Sulfidization was necessary for the flotation of the oxides of both lead and zinc and willemite. Two types of sulphidization agents were used for the same which are elemental sulfur and sodium sulphide (Na2S) which were mixed with the slag during ball milling. The effect of sulfidizing agent is shown in the figure 3.

[057] Although previous studies have reported that the sulfidization with sodium sulfide was necessary for floating willemite, but the present study showed that the silicates (Willemite and Hardystonite) in the present material (a mixture of silicates and oxides) did not respond to the sulphidization (figure 3 (a)). Also, the recovery and grade of lead post sulphidization was increased as observed in fig 3(b)-(c). Sulfidizing agents converted lead oxide to lead sulphides which gets floated up. Also, it was observed that elemental-sulfur works better comparatively to sodium sulfide as the later decreased the zinc recovery by flotation to an extent.

Effect of Collectors:
[058] Apart from sulfidization which increases the electronegativity of the mineral and favors the attraction between the collector and the mineral, two different collectors were used for improving the flotation and enhancing the recovery. The effect of different collectors were shown in figure 4.

[059] Cationic collector Octadecyl amine (Octa) was used for the flotation of zinc silicate minerals as given in previous studies and was added to effectively increase willemite floatation for increased Zn recovery. Two collectors i.e. PAX (Potassium Amyl Xanthate) and SiPX (sodium isopropyl xanthate) were used along with Octa. It was observed that SiPX and PAX did not affect the lead recovery, however, decreased Zn recovery and mass pull as shown in figure 4(a). On the other hand, although the zinc grade in the concentrate dropped on addition of PAX, but the lead grade was increased as shown in figure 4(b). Therefore, PAX was a better lead sulphide collector compared to SiPX.

Effect of Zn depressant:
[060] Apart from recovery another important aspect of flotation was the concentration of a particular element of interest produced in the concentrate as it governs the next stage of processing in the plant. During flotation, sometimes the concentration of one element was improved by depressing another element. To understand whether the similar observation was occurring in the phase separated slag, zinc sulphate (a zinc depressant) was used and the effects of ZnSO4 on various sulphidation agents on the floatation were shown in figure 5.

[061] It was observed that ZnSO4 played a dominant role in improving the grade of Pb in the concentrate as shown in figure 5(a). Also, in contrast to the previous analysis as shown in figure 3(a), with addition of ZnSO4, Na2S was promoting more Willemite and Hardystonite floatation as shown in figure 5(b).

Effect of Double Stage flotation:
[062] Two stage flotation was performed to obtain lead and zinc concentrate separately using variation in sulphidation agents (Na2S, Ele-S) and also lead promoter ethylene diamine tetra acetic acid (EDTA). In the comparison study sulphidizing and lead promoter were added in the 1st stage of flotation along with ZnSO4 and PAX to obtain lead rich concentrate. In the 2nd stage of flotation, CuSO4, Octa and PAX were used to obtain Zinc rich concentrate. The effect of sulphidizing agent and lead promoter were shown in figure 6.

[063] The above study represents a novel way of recovering lead and zinc from lead smelter slag by improving the grade by the combined process of slow cooling, sulphidization and subsequent flotation. This is because the slag from smelter is normally pelletized and quenched with water to enable easy handling. However, the present inventors have found that this inhibits the phase separation on sufficient scale that is required for liberation of constituents on grinding. Minerology studies show that while the water quenched slag is homogenous, replacement by the slow cooling of the molten lead smelter slag from furnace discharge clearly shows the presence of separate phases of various oxides (lead and zinc oxides), silicates (Hardystonite and Willemite) along with some mixed oxide phase. Such slow cooling need not be an additional heating and cooling step, but it was integrated with the process of slag draining from the lead smelter, by diverting to slag pots and allowing to cool naturally. In the subsequent grinding process, addition of sulphidizing agents like sodium sulphide (Na2S) and elemental-sulfur helps in conversion of the oxides of lead to sulphides, thereby helping in the high recovery (~ 65%) and high grade (~20%) of the lead in successive flotation processes. Addition of collectors like SiPX and PAX improves lead grade % (around 12 wt%) in the concentrate keeping recovery almost constant, but on the contrary decreases the zinc recovery %. PAX is more effective than SiPX. Addition of Zinc depressants like ZnSO4 suppresses the zinc grade% in the concentrate but increases the lead grade% in the concentrate. Zinc could be separated into a ZnO/ZnS rich phase and a silicate rich phase, offering opportunity for further extraction. In double step flotation process also, we have achieved higher Pb grade (approx. 5 times) w.r.t the base material. The grades of the lead and zinc mineral concentrates can be further improved by standard flotation steps like cleaners.

ADVANTAGES OF THE PRESENT INVENTION

[064] The process of the present disclosure has the following advantages:
• Greener process; less CO2 producing;
• Less energy intensive;
• Cost-effective;
• Results in high recovery rate of the metal concentrate;
• Convenient to use;
• Slag is cooled after withdrawing from the furnace, thus allows for other process to be carried out simultaneously.

SPECIFIC EMBODIMENTS OF THE PRESENT DISCLOSURE

[065] The present disclosure relates to a process of separating at least one of lead and zinc concentrate from smelter slag comprising the steps of:
i. draining a slag directly from the smelter and cooling the drained slag naturally in air;
ii. grinding and sulfidizing the cooled slag; and
iii. froth floating the sulphidized slag to obtain the lead and/or zinc concentrate.

[066] Such process is disclosed, wherein cooling of the drained slag comprises cooling naturally in air at ambient temperature.

[067] Such process is disclosed, wherein grinding and sulfidizing the cooled slag comprises either co-grinding the cooled slag with a sulfidizing agent or grinding the cooled slag followed by sulfidizing the grounded slag with the sulfidizing agent.

[068] Such process is disclosed, wherein the smelter slag comprises Hardystonite (Ca2ZnSi2O7), Willemite (Zn2SiO4), Zinc Oxide (ZnO), Iron oxide (FeO), Melilite, Lead oxide (PbO), Zinc sulphide, and lead sulfide.

[069] Such process is disclosed, wherein the sulfiding agent is selected from the group consisting of sodium sulfide (Na2S), elemental sulfur, ammonium sulphide ((NH4)2S), sodium hydrogen sulphide (NaSH), calcium sulphide (CaSx), and a combination thereof.

[070] Such process is disclosed, wherein step of froth flotation is carried out in single stage circuit or double stage circuits comprising addition of iron and zinc depressant, lead and zinc promoter, zinc activator, collector, and frother.

[071] Such process is disclosed, wherein the frother is selected from the group consisting of pine oil, methyl isobutyl carbinol (MIBC), and a combination thereof.

[072] Such process is disclosed, wherein the collector is selected from the group consisting of potassium amyl xanthate (PAX), sodium isopropyl xanthate (SiPX), Octadecyl amine, sodium ethyl xanthate, sodium isobutyl xanthate, potassium ethyl xanthate, and a combination thereof.

[073] Such process is disclosed, wherein the lead and zinc promoter is selected from the group consisting of dithiophosphate (DTP), monothiophosphate, thionocarbamate, dithiophosphinate, and a combination thereof.

[074] Such process is disclosed, wherein the zinc depressant is zinc sulphate (ZnSO4) and the iron depressant is sodium cyanide (NaCN) or Na-metabisulfite

[075] Such process is disclosed, wherein the zinc activator is copper sulphate (CuSO4).
, Claims:We Claim:

1. A process of separating at least one of lead and zinc concentrate from smelter slag comprising the steps of:
(A) draining a slag directly from the smelter and cooling the drained slag naturally in air;
(B) grinding and sulfidizing the cooled slag; and
(C) froth floating the sulphidized slag to obtain the lead and/or zinc concentrate.

2. The process as claimed in claim 1, wherein cooling of the drained slag comprises cooling naturally in air at ambient temperature.

3. The process as claimed in claim 1, wherein grinding and sulfidizing the cooled slag comprises either co-grinding the cooled slag with a sulfidizing agent or grinding the cooled slag followed by sulfidizing the grounded slag with the sulfidizing agent

4. The process as claimed in claim 1, wherein the smelter slag comprises Hardystonite (Ca2ZnSi2O7), Willemite (Zn2SiO4), Zinc Oxide (ZnO), Iron oxide (FeO), Melilite, Lead oxide (PbO), Zinc sulphide, and lead sulfide.

5. The process as claimed in any one of claims 1 or 3, wherein the sulfiding agent is selected from the group consisting of sodium sulfide (Na2S), elemental sulfur, ammonium sulphide ((NH4)2S), sodium hydrogen sulphide (NaSH), calcium sulphide (CaSx), and a combination thereof.

6. The process as claimed in claim 1, wherein step of froth flotation is carried out in single stage circuit or double stage circuits comprising addition of iron and zinc depressant, lead and zinc promoter, zinc activator, collector, and frother.

7. The process as claimed in claim 6, wherein the frother is selected from the group consisting of pine oil, methyl isobutyl carbinol (MIBC), and a combination thereof.

8. The process as claimed in claim 6, wherein the collector is selected from the group consisting of potassium amyl xanthate (PAX), sodium isopropyl xanthate (SiPX), Octadecyl amine, sodium ethyl xanthate, sodium isobutyl xanthate, potassium ethyl xanthate, and a combination thereof.

9. The process as claimed in claim 6, wherein the lead and zinc promoter is selected from the group consisting of dithiophosphate (DTP), monothiophosphate, thionocarbamate, dithiophosphinate, and a combination thereof.

10. The process as claimed in claim 6, wherein the zinc depressant is zinc sulphate (ZnSO4) and the iron depressant is sodium cyanide (NaCN) or Na-metabisulfite

11. The process as claimed in claim 6, wherein the zinc activator is copper sulphate (CuSO4).