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How to Process Lead-Zinc Ore by Gravity and Froth Flotation

Author : Jordan | Last Updated :

Lead and zinc are extremely close in nature, especially in primary deposits, and are often symbiotic. Lead-zinc ore is a mineral resource rich in lead and zinc.

In nature, there are about 250 types of lead-zinc minerals discovered, of which about 1/3 of the minerals are sulfides and sulfates, with galena and sphalerite being the most important.

Lead-zinc ore: a mineral resource rich in lead and zinc

Lead-zinc ore: a mineral resource rich in lead and zinc

Lead-zinc ores generally have to go through beneficiation into concentrates to smelt lead and zinc metal products, which are widely used in the chemical industry, such as the mechanical and chemical industry, petrochemical industry and so on. The beneficiation process of lead-zinc ore is generally crushing, grinding, gravity separation for waste disposal and froth flotation.

Crushing section and equipment

The three-stage one closed circuit crushing section is currently the most widely used crushing process in large and medium-sized lead-zinc concentrators.

Coarse crushing section: The lead-zinc ores are pre-screened by a vibrating screen, then the products on the vibrating screen enter the jaw crusher to be coarsely crushed.

Medium crushing section: Products under the vibrating screen and coarsely crushed lead-zinc ores enter the vibrating screen for the second pre-screening. The products on the screen are crushed in the cone crusher.

Three-stage one closed-circuit crushing process and equipment

Three-stage one closed circuit crushing process flowsheet

Fine crushing section: Products under the screen and the ores have been medium crushed enter the third screen together. The products on the screen enter the cone crusher for fine crushing, then the fine crushing products return to the vibrating screen for screening, forming a closed-circuit process.

While products under the screen enter the grinding stage. The grain size of the ores is generally 0-15 mm.

Tip: When the content of fine ores (0-3 mm) account for more than 5% of the original ore, among which 200 mesh particles account for about 10%, and the water content exceeds 8%~10%, to ensure smooth ore crushing and avoid the blockage of silo, desliming or ore washing by sand washing machine is necessary before coarse or fine crushing.

The products under the ore washing screen (usually -7 mm) enter the spiral classifier. The sand returned enters into the fine ore bin, while the overflow after concentration is combined with the overflow of the classifier in the first grinding stage.

Grinding and classification process and equipment

The grinding equipment of the lead-zinc ore dressing plant is mainly spiral classifiers and ball mills.

Because of its high density and low hardness, lead ore is easy to be over-grinded. To improve grinding conditions and increase the recovery rate of ore dressing, some concentrators adopt stage grinding and stage separation circuit to re-grind and re-concentrate tailing after roughing.

Using such grinding and dressing circuit can not only prevent the ore from grinding to the monomer dissociation at one time and cause the coarse-grained minerals to be over-crushed, but also solve the problem of insufficient grinding that cannot achieve monomer dissociation.

Grinding and classification process and equipment

Grinding and classification process and equipment

The first stage of grinding: Send the lead-zinc powder of 0-15 mm screened by the vibrating screen evenly to the ball mill for grinding. After the first stage of grinding, control the classification by the spiral classifier to increase the amount of sand returned by the first stage of ball mill.

The second stage of grinding: The overflow particle size of the second stage of grinding increases from -0.074 mm accounting for 78% to more than 85%, which significantly reduces the aggregates of sphalerite and galena in rough lead concentrates.

The third stage of grinding: The rough lead concentrates enter the third stage of grinding to be ground to -0.043 mm, accounting for 95%, to achieve full dissociation of lead-zinc minerals.

Re-grinding and re-concentration of tailings: Concentrated tailings will return to the lead coarse selection as middlings in lead concentration. Rough zinc concentrates, as rough lead concentrates, are re-ground and re-concentrated. Thus, the problems of uneven embedding and sorting of metallic minerals are solved effectively.

Pretreatment and discarding process and equipment for lead-zinc ore

For coarse-grained or aggregate disseminated lead-zinc ore, pre-selection and waste disposal measures with large production capacity and low beneficiation costs are often adopted to discard a large amount of gangue and surrounding rock waste in advance.

Pretreatment and discarding process and equipment for lead-zinc ore

Pretreatment and discarding process and equipment for lead-zinc ore

Gravity beneficiation is a common method using a heavy liquid with appropriate specific gravity to make the lighter minerals float up while the heavier minerals sink. The dense medium of heavy liquid mainly includes ferrosilicon, magnetic ore powder, barite, furnace ash, pyrite and so on.

  1. 1 The lead-zinc ores are coarsely crushed by a jaw crusher, then screened by the screening machine.
  2. 2 The products on the screen are sent to the spiral chute for heavy medium separation, while the floating ores are discarded as tailings.
  3. 3 The sinking ore and the products under the sieve are sent to a ball mill for grinding, then lead and zinc are respectively floated to obtain lead concentrate and zinc concentrate.

Fote lead-zinc ore gravity separation case in South Africa

A lead-zinc mine in South Africa is mainly composed of three sulfide minerals: galena, sphalerite and pyrite. Among them, the contents of sphalerite are the most, galena and pyrite are relatively less. The mineral composition of the ore is as follows:

Minerals Galena Sphalerite Pyrite Gangue
Low grade 1.8 8.0 6.0 84.1
Middle grade 3.2 11.6 4.6 80.6
High grade 4.2 14.7 3.6 77.6

Through the heavy medium separation process, 41.55% of floating ores can be discarded in advance, which can effectively reduce the amount of grinding and improve the grade of selected ores. Finally, the sinking ores and fine ores with a yield of 58.45% can be obtained.

Fote lead-zinc ore gravity separation case in South Africa

Fote lead-zinc ore gravity separation case in South Africa

The grade and recovery rate of lead and zinc are as follows:

Minerals Lead Zinc
Grade of raw ore 1.77% 4.15%
Grade of concentrate 2.92% 6.50%
Recovery rate 96.5% 91.5%

Flotation process and equipment of lead-zinc ore

In the beneficiation of lead-zinc ore, flotation is an important process.

Mixing in mixing tank: After the ground pulp is classified by the classifier, it enters the mixing tank for mixing. Control the slurry concentration at 25-35%, then add flotation agent to control the slurry pH value 9-11 and stir it for 6-15 min.

Flotation process and equipment of lead-zinc ore

Flotation process and equipment of lead-zinc ore

Agents adding: Pour the well-stirred lead-zinc slurry directly to the flotation machine, and inhibit zinc by inhibitors. Add lead collectors firstly to collect the lead, then add activator to activate zinc, finally use zinc collectors to collect zinc.

Concentration: The entire flotation process needs to go through a rough selection, two concentrations and three concentrations to obtain higher-grade lead and zinc concentrates.

Concentration and drying: The lead-zinc concentrates after flotation contain certain moisture, which need to be concentrated and precipitated in the thickener, and then dried and dehydrated by the dryer to obtain the finished lead-zinc concentrates.

Fote lead-zinc ore flotation case in India

The concentrator of a lead-zinc mine in India contains 9.53% of lead, 6.37% of zinc and 13.28% of sulfur. The ore is characterized by high sulfur content.

The phase composition of lead-zinc minerals:

Phase Lead mineral Zinc mineral
Lead in lead sulfide Lead in lead oxide Total lead Zinc in zinc sulfide Zinc in zinc oxide Total zinc
Content 9.05 0.48 9.53 6.06 0.31 6.37
Occupancy 94.96 5.04 100.0 95.13 4.87 100.0

Flotation scheme:

Fote lead-zinc ore flotation case in India

Fote lead-zinc ore flotation case in India

Under the condition that the raw ore contains 9.53% of lead, 6.37% of zinc, 13.28% of sulfur, and -0.074 mm ore is accounting for 78%, after one roughing, two sweepings, two beneficiations of lead, as well as one roughing, two sweepings sand three beneficiations of zinc, customers can obtain:

Minerals Lead concentrates Zinc concentrates
Lead 50.57% 1.98%
Zinc 2.02% 48.28%
Recovery rate 91.72% 90.56%

Fote lead-zinc mine flotation case in Peru

The main chemical composition (%) of a lead-zinc mine in Peru is: 3.94 of lead, 7.23 of zinc, and 17.85 of iron. The main minerals of the original ore are 5.1% of galena and 15.0% of sphalerite.

The ore is characterized by a high lead-zinc oxidation rate (10-30%) and a large amount of easy-floating pyrite (20-30%). The zinc is mainly in sphalerite.

The original production process is "concentration of lead, bulk flotation of zinc and sulfur". The total recovery rate of silver in lead and zinc concentrate is 50-60%. The process index is as follows:

Minerals Lead concentrate Zinc concentrate
Grade 62.07% 42.71%
Grade of concentrate 2.92% 6.50%
Recovery rate 76.31% 73.06%

Flotation scheme:

Fote lead-zinc mine flotation case in Peru

Fote lead-zinc mine flotation case in Peru

Fote focuses on the comparison of schemes, investment costs and comprehensive utilization of minerals when processing lead-zinc ores, therefore we improve the flotation process and propose selective flotation of lead and zinc. With the concentrate grade basically unchanged, the total recovery rate of lead and zinc has increased by nearly 3%.

Fote lead-zinc ore flotation case in the U.S.

The content of a lead-zinc mine in the United States is as follows:

Minerals Lead Zinc Iron Sulphur
Content 3.26% 2.54% 18.02% 27.33%

The zinc in ores mainly exists in the form of zinc sulfide, and the distribution rate of zinc sulfide in the zinc phase is 78.26%.

Lead mainly exists in the form of lead sulfide, and a small amount of lead sulfate. In addition, the ore also contains pyrite, silicon oxide and calcium carbonate.

Flotation scheme:

Fote lead-zinc ore flotation case in the U.S.

Fote lead-zinc ore flotation case in the U.S.

For the raw ore containing 3.26% of lead and 2.54% of zinc, Fote adopts a lead-zinc bulk flotation process to finally obtain a lead-zinc mixed concentrate with a comprehensive grade of about 43% (of which lead contains about 25% and zinc 18%).

The comprehensive recovery rate of lead and zinc is about 85%, which is far greater than that of the lead-zinc concentrator provided (70% lead and 60% zinc) when the selective flotation process was used.

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Author : Jordan Jordan is the writer of the blog with a broad knowledge of this industry. Most importantly, he hopes to help you in your projects sincerely.

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