The Basics of How Ore Processing and Recovery Plants Work

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Mar 15,

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Ore Processing & Recovery Plant, Savona Equipment

The Basics of How Ore Processing and Recovery Plants Work

The term processing and recovery plant is broad to say the least so we are going to give some basic examples of the types of ore processing plants. It is important to understand that each full scale production, ore processing plant, backfill plant, placer mining plant, or even a small scale test plant is specifically engineered for the material it will be processing. The type of plant at any given mine or recovery operation also depends on permits, available road access, amount of precious materials to be mined, and of course cost. In this article we will be focusing on ore processing plants.

What kind of material are you processing?

Technically all ore processing falls under the field of extractive metallurgy, mineral engineering, mineral processing, also known as mineral dressing or ore dresing . It is the process of separating commercially valuable minerals from their ores. Commonly, haul trucks transport the ore from open pits or underground operations to processing operations. Some ores may be stockpiled for later processing. The grade and type of ore determine the mineral processing method used. Additionally, the geochemical makeup of the ore, including its hardness, sulfur content, carbon content and other minerals found within, impact the cost and methods used to extract gold, silver, and other precious metals and minerals.

What can you recover?

Ore processing recovery systems are used for everything from recovering precious metals, industrial minerals to processing rare earth minerals. Plants for recovering precious metals often recover multiple metals or minerals in the same operation. This is because often where there is gold you will find copper and silver. When we talk about recovering precious metals we are identifying what are also known as noble metals like gold, silver, platinum, and palladium. Other primary metals that ore processing plants are used to recover include copper and iron ore. There are also rare metallic minerals like nickel, cobalt, and scandium which are mined using similar processes. There is also the processing of rare earth minerals.

How much material will an ore processing plant process per day?

Ore & Mineral Processing Plants are designed for various purposes and capacity, for large primary ore processing, secondary, and tertiary fine material concentrating as well as complete aggregate, recycling, mining, and treatment facilities. They are mostly measured by TPD (tons per day). Based on the capacity of the plant and the grade of the ore it is processing, engineers and mining geologists can determine the economic viability of the mine. The investment made in a gold processing plants, silver processing plants, as well as plants for recovery of other precious metals and rare earth minerals is impacted by the cost and methods used to extract gold, silver, and other precious metals and minerals. It is also impacted by the market price and market projections of the material being mined. A TPD Gold & Silver Processing Plant will cost millions of dollars where small mineral pilot plants may cost hundred of thousands and a portable pilot plant may cost only thousands. Many full scale operations begin with a test plant before upgrading to a full production ore processing plant.

What equipment is included in an Ore Processing Plant?

Each plant is different but there are several common pieces of equipment you will almost always find through 5 stages of processing. The first is size reduction meant to break up the largest of material which includes crushers, industrial screens, and large hoppers and feeders. The second process is the gravity circuit which further breaks down the material for further processing and includes grinding mills, cyclones, and depending on the process gravity concentrators. The third is the leaching process that uses equipment with industrial grade agitators and mixers and contains a leaching solution and allows the valuable material to leach from the ore into solution. The fourth stage is the actual recovery of the material being processed which greatly depends on the material itself and the ore it is mixed with. For gold it could be a refining and smelting system, bullion furnace, or concentrating tables. The fifth stage is the tailings treatment. Tailings are the byproducts left over from mining and extracting resources, such as extracting bitumen from the oilsands or minerals such as copper or gold from ores. Tailings include: Finely ground rock particles &#; ranging from sand-sized to silt-sized. Chemicals used to extract the valuable mineral or oil. The treatment is meant to process the tailings remove the sediments and chemicals and then often reuse the water for going back into the processing plant. Mixed in with the entire process are various types of industrial pumps, belt conveyors, electrical equipment including large generators, and heavy equipment.

How can you purchase an Ore Processing Plant?

There are many ways to purchase a plant. Large scale mines will often engineers and new plant. In some case publicly traded companies require new processing equipment for the main components of the plants. A second common option is to buy a used plant that has already been in service. This can often greatly reduce the cost while still getting a plant that is engineered as well as proven to operate efficiently. It also minimizes the lead times of waiting for new equipment to be manufactured. The third option is to buy each piece of mining and milling equipment individually and mix new and used equipment. This can lead to even a further reduction in your cost but can be a challenge to find each piece of equipment that will fit your specifications.

This article is a brief overview of an ore processing and recovery plant. The first step is to speak with a reputable professional in the industries including mine engineers, mining geologists, and equipment experts. Once you have the right team in place it will be much easier to find the right equipment and purchase the plant which produces the highest profits.

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Process of refining lead metal

The now closed Doe Run primary lead smelting facility in Herculaneum, Missouri

Plants for the production of lead are generally referred to as lead smelters. Primary lead production[clarification needed] begins with sintering. Concentrated lead ore is fed into a sintering machine with iron, silica, limestone fluxes, coke, soda ash, pyrite, zinc, caustics or pollution control particulates. Smelting uses suitable reducing substances that will combine with those oxidizing elements to free the metal. Reduction is the final, high-temperature step in smelting. It is here that the oxide becomes the elemental metal. A reducing environment (often provided by carbon monoxide in an air-starved furnace) pulls the final oxygen atoms from the raw metal.

Lead is usually smelted in a blast furnace, using the lead sinter produced in the sintering process and coke to provide the heat source. As melting occurs, several layers form in the furnace. A combination of molten lead and slag sinks to the bottom of the furnace, with a layer of the lightest elements referred to as speiss, including arsenic and antimony floating to the top of the molten material. The crude bullion and lead slag layers flow out of the 'furnace front' and into the 'forehearth', where the two streams are separated. The lead slag stream, containing most of the 'fluxing' elements added to the sintering machine (predominantly silica, limestone, iron and zinc) can either be discarded or further processed to recover the contained zinc.

The crude lead bullion, containing significant quantities of copper will then undergo 'copper drossing'. In this step elemental sulphur, usually in solid form is added to the molten crude lead bullion to react with the contained copper. A "matte" layer forms in this step, containing most of the copper originating from the crude lead bullion and some other impurities as metal sulfides. The speiss and the matte are usually sold to copper smelters where they are refined for copper processing.

The lead from the blast furnace, called lead bullion, then undergoes the drossing process. The bullion is agitated in kettles then cooled to 700-800 degrees. This process results in molten lead and dross. Dross refers to the lead oxides, copper, antimony and other elements that float to the top of the lead. Dross is usually skimmed off and sent to a dross furnace to recover the non-lead components which are sold to other metal manufacturers. The Parkes process is used to separate silver or gold from lead.

Finally, the molten lead is refined. Pyrometallurgical methods are usually used to remove the remaining non-lead components of the mixture, for example the Betterton-Kroll process and the Betts electrolytic process. The non-lead metals are usually sold to other metal processing plants. The refined lead may be made into alloys or directly cast.[1]

People who operate or work in such plants are also referred to as smelters.

Lead ores

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Evolution of the extracted lead ores grade in different countries (Canada, Australia).

Galena, the most common mineral of lead, is primarily lead sulfide (PbS). The sulfide is oxidized to a sulfite (PbSO3) which thermally decomposes into lead oxide and sulfur dioxide gas. (PbO and SO2) The sulfur dioxide (like the carbon dioxide in the example above) is expelled, and the lead oxide is reduced. Anglesite, Cerussite, Pyromorphite, Mimetite and Wulfenite are other lead ores.

Other elements frequently present with lead ores include zinc and silver.[2]

Secondary lead processing

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Most of the lead produced comes from secondary sources. Lead scrap includes lead-acid batteries, cable coverings, pipes, sheets and lead coated, or terne bearing, metals. Solder, product waste and dross may also be recovered for its small lead content. Most secondary lead is used in batteries.

To recover lead from a battery, the battery is broken and the components are classified. The lead containing components are processed in blast furnaces for hard lead or rotary reverberatory furnaces for fine particles. The blast furnace is similar in structure to a cupola furnace used in iron foundries. The furnace is charged with slag, scrap iron, limestone, coke, oxides, dross, and reverberatory slag. The coke is used to melt and reduce the lead. Limestone reacts with impurities and floats to the top. This process also keeps the lead from oxidizing. The molten lead flows from the blast furnace into holding pots. Lead may be mixed with alloys, including antimony, tin, arsenic, copper and nickel. It is then cast into ingots.[3][4]

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Lead exposure

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Humans have been smelting lead for thousands of years, poisoning themselves in the process. Although lead poisoning is one of the oldest known work and environmental hazards, the modern understanding of the small amount of lead necessary to cause harm did not come about until the latter half of the 20th century. No safe threshold for lead exposure has been discovered&#;that is, there is no known amount of lead that is too small to cause the body harm.

The US Centers for Disease Control and Prevention and the World Health Organization state that a blood lead level of 10 μg/dL or above is a cause for concern; however, lead may impair development and have harmful health effects even at lower levels, and there is no known safe exposure level.[5] Authorities such as the American Academy of Pediatrics define lead poisoning as blood lead levels higher than 10 μg/dL.

Lead smelters with little pollution controls contribute to several environmental problems, especially raised blood lead levels in the surrounding population. The problem is particularly significant in many children who have grown up in the proximity to a lead smelter.[6]

History

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The earliest known cast lead beads were thought found in the Çatalhöyük site in Anatolia (Turkey), and dated from about  BC. They were later identified in fact to be made from cerussite and galena, minerals rich in, but distinct from, lead.[7] Ancient smelting was done using loads of lead ore and charcoal in outdoor hearths and furnaces.

Although lead is a common metal, its discovery had relatively little impact in the ancient world. It is too soft to be used for weapons (except possibly as sling projectiles) or for structural elements. However, being easy to cast and shape, it came to be extensively used in the classical world of Ancient Greece and Ancient Rome for piping and storage of water. It was also used as a mortar in stone buildings, and as a writing material. Smeltmills were water-powered mills used to smelt lead or other metals. The Roman lead smelting has led to evidence of global pollution. Greenland ice cores from 500 BCE to 300 CE show measurably elevated lead content in the atmosphere.[8] Researchers studying an ice core from Colle Gnifetti, in the Swiss part of the Monte Rosa massif, have found that higher historical European airborne lead pollution levels are associated with changes in the monetary system from gold to silver from the year 640 CE, with the principal source likely to be the Melle mines in France. Later airborne pollution, between the years and CE, correlates even more strongly with contemporaneous records of lead and silver production from mines in the Peak District of England, at levels similar to those seen in the Industrial Revolution.[9][10][11]

Georgius Agricola (&#;) presented details of lead smelting methods and facilities current in Europe in the first half of the 16th century in Book IX of his treatise on mining and metallurgy, De Re Metallica. Methods ranged from primitive open-hearth arrangements (essentially bonfires on which lead ore was piled) to blast furnaces capable of continuous operation.[12]

In the USA there are 400 forgotten lead smelting firms that operated in the s to s and may have deposited dangerous levels of lead contamination in nearby soil.[13]

Historic mining and smelting sites

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Asia

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Australia

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Europe

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North America

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South America

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Active lead mines and smelters

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Doe Run lead smelter in Herculaneum, Missouri

Africa

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• Rönnskär copper smelter is in Skelleftehamn, Sweden and its main products are copper, zinc clinker, lead and precious metals.
• Bergsöe lead smelter outside Landskrona in southern Sweden extracts lead from scrap car batteries.
• Tara Mine
• KCM in Plovdiv which has produced lead for over 60 years using a blast furnace and is now in the process of bringing a new 60 million euro smelter TSL furnace online in order to replace the ageing blast furnace.

See also

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References

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