Zinc and Lead Mining

Zinc and Lead Mineral Processing

Zinc and Lead Mineral Processing

Lead and zinc ore are common symbiotic associated minerals, they often appear at the same time. Lead-zinc Ore is the main ore for refining lead and zinc metal. It is the main technical process to refine lead first and then zinc in the lead-zinc ore beneficiation.

Zinc and Lead Mineral Processing Flow:
Generally Zinc and Lead Mineral Processing adopts one closed-circuit three process crushing, two closed-circuits two process grinding, one rough crushing three fine grinding three scavenging lead flotation process,one rough crushing three fine grinding three scavenging zinc flotation process.

The detailed process is as follows: the raw material is send to the rough crusher by the vibrating feeder, then to the fine crusher. After that, the raw material comes to screen, at this process, the material on the screen(big granules) will go back to the fine crusher for a second crushing. And the material below the screen is acceptable product which can be transferred to the fine ore bin. Under the bin there should be a feeder, the fine ore is send to the first stage ball mill by the belt conveyor, further to the second stage ball mill. Then the material comes to the first stage hydrocyclones. The setting material in the hydrocyclones goes back to the second stage mill for a further grinding. The material in the first hydrocyclone overflows to the second stage hydrocyclone. The setting material in the second stage hydrocyclone goes back to the third stage mill for a further grinding. Then material in the third stage mill is sent again to the second stage hydrocyclone and overflows to two agitators. After adding chemicals to the agitators, it comes to the one rough crushing three fine grinding three scavenging lead flotation process. At this time, the tailing and scavenger concentrate failings go back to the former stage. The lead concentrate is separated out in the third beneficiation process, and is sent to the setting pond. The tailings of lead flotation come to the agitators. By adding chemicals again to the agitators, it comes to another process of zinc flotation. At this time, the tailings and scavenger concentrate tailings go back to the former stage. The zinc concentrate is separated out in the third beneficiation process, and is sent to the setting pond. Tailing of zinc flotation is the final tailing which is sent to the tailing yard after concentration. The water from concentration and filteration can be reused.

Zinc and Lead Mineral process and concentrates by Flotation separation and recovery from ores containing galena (PbS) and sphalerite (ZnS) is well established and generally achieved quite effectively. Silver often provides highly significant economic value, if not the greatest value, with the silver most often associated with the galena mineralization which is fortuitous since smelters pay more for silver in lead vs. zinc concentrates. The non-values include iron sulphides such as pyrite and pyrrhotite that, while are often floatable, can be controlled. Siderite, an iron carbonate mineral, is often also associated in at least some minor quantity.

Marmatite ((Zn,Fe)S) is an iron-rich sphalerite which consequently results in lower zinc concentrate grades. Marmatite concentrates have a lower zinc level due to dilution from the iron minerals.

Lead flotation collectors and frother are conditioned before lead flotation which is conducted typically at near neutral to slightly elevated pH which can be increased in the cleaner circuit to ensure iron sulphide rejection. Sometimes cyanide, if can be used, is added to help depress iron sulphides. Because silver typically is mineralogically associated with galena, most of the silver values are carried with and report to the galena concentrate.

Sphalerite that is rejected into the lead flotation tails is then floated in a second flotation step after activation with copper sulphate. The copper ions replace zinc atoms on the sphalerite surface creating a pseudocopper mineral surface coverage on the sphalerite which is then collected using copper flotation type collectors. Because most of the iron sulphides also report to the lead flotation tails and so feeds the zinc flotation circuit, typically lime is used to raise pH for iron sulphide depression. The flotation collectors used in sphalerite flotation tend to be less powerful because sphalerite at this stage typically readily floats and using a more aggressive collector can float more non-sphalerite minerals.

Optimum lead concentrate metallurgy and recoveries are usually achieved using a combination of a xanthate and dithiophosphates. If the galena surfaces are slightly oxidized (“tarnished”), including mercaptobenzothiazole (MBT) is often made part of the collector suite to maximize galena recoveries. Frothers used in galena flotation tend to be of the weaker type, such as MIBC, because galena is readily floatable and have high flotation kinetics. However, because of the high float kinetics and high galena mineral density, the mineral froth carrying capacity may necessitate use of a slightly stronger frother or a combination with a stronger frother component for achieving optimum metallurgical results.

In rare circumstances, mineralogy and metallurgical response considerations necessitate an initial bulk lead-zinc concentrate with the lead and zinc minerals subsequently separated in a selective flotation step. Under this scheme, a bulk galena and sphalerite flotation concentrate is produced at pH 6.5 (modified with H2SO4) with some copper sulphate addition to ensure full sphalerite activation. The bulk concentrate is subsequently conditioned with sodium hydroxide to achieve an approximate 11.5 pH and collector addition from which a lead concentrate is floated. The zinc concentrate is actually the tails from this bulk separation step. The flotation tailing is the zinc concentrate. If the silver is associated with the galena, the silver reports to the lead concentrate.

While pyrite is fairly easy to depress with lime, pyrrhotite is more difficult to depress. An alternative to metabisulphide depression is to aerate the slurry which, if the pyrrhotite is reactive, can render this iron sulphide less floatable. In cases of greater iron sulphide depression challenges, the zinc concentrate can be cleaned by reverse flotation of the concentrate by first treating with SO2 to reduce pH to 5-5.5 and then heating the pulp to 60-70 degrees C. The gangue is floated with the sphalerite reporting tothe tails

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