Non-ferrous metallurgical processing

Lime products play a key role in the mining and extraction of non-ferrous metals, including aluminum, copper, gold, nickel, cobalt, uranium, titanium and lithium. Lime is also important for the pyrometallurgical refining and smelting of several non-ferrous metals. In addition, lime products are used in effluent and tailings treatment, and in settling, dewatering, filtration, environmental protection and mine safety.

Lhoist offers a wide range of lime products of appropriate purity and reactivity for process optimization and metal recovery. Experts in lime utilization efficiency, we bring innovation and expertise to our customers through customized services. These range from lime product reagent supply to outsourced lime-slaking units for producing milk-of-lime (slaked lime slurry) at customer sites.

Lime utilization efficiency, or consumption performance, in metallurgical processing is dependent on numerous factors other than the CaO content of the lime. This video explains the role of lime slaking and the resulting Ca(OH)2 particle size on lime utilization efficiency. For detailed scientific information on this topic follow this link: https://doi.org/10.1016/j.hydromet.2017.09.001

Extractive metallurgy, hydrometallurgy and mineral processing

Safety & process applications

Pyrometallurgical refining and smelting

Extractive metallurgy, hydrometallurgy and mineral processing

Base metal concentrate production by mineral flotation

The mineral separation method of flotation (to produce sulfide mineral concentrates) relies on the principle that different mineral surfaces react differently at different pH levels. By using lime for pH control, differential mineral flotation behaviors can be achieved to concentrate and selectively recover the valuable base-metal sulfides (copper, nickel, cobalt, zinc and lead).

Pyrite depression during sulfide mineral flotation

During flotation, pyrite FeS₂ – the most abundant but least valuable sulfide mineral – must be separated from valuable base-metal sulfides, such as chalcopyrite CuFeS₂. Without pyrite depression the FeS₂ would contaminate and dilute the concentrate product. The use of lime facilitates this separation.

Alumina production from bauxite using Bayer processing

The Bayer process is the principal industrial method for refining bauxite to produce alumina (aluminum oxide). Lime, typically in the form of slaked lime (milk of lime), is used in several components of mineral processing. These include digestion, causticisation, filtration, filter-aid production (tri-calcium aluminate formation) and oxalate removal.

Gold recovery by cyanidation

Cyanide is the most commonly-used lixiviant for the recovery of gold into solution, from which it can be recovered and converted into gold metal. Playing a key role in controlling the cyanidation leaching process, lime increases the pH to an effective and safe operational level.

Refractory gold treatment

Refractory gold ore generally contains iron sulfide (typically pyrite, FeS₂), which needs to be oxidized and removed prior to cyanidation. All the various oxidation methods generate acid, requiring significant levels of lime consumption for acid neutralization, impurity precipitation and pH control (>10.5) for cyanidation. We can maximize lime utilization efficiency for these applications.

Arsenic removal

Arsenic is a significant and hazardous impurity associated with many copper and refractory gold ores. Often present in acid solutions, it must be removed into a stable solid form. The conversion of soluble arsenic into scorodite FeAsO₄.2H₂O is considered the most suitable treatment option. It requires the following elements:

Soluble ferrous iron
An oxidant to oxidize ferrous to ferric iron. This results in the co-oxidation of arsenic to arsenate and the co-precipitation of As with Fe in the form of scorodite.
Lime to increase the pH of the acidic arsenic-containing solution. This facilitates the oxidation of ferrous to ferric iron and ensures the precipitation and stability of the scorodite.

Copper-cobalt oxide ore leaching

Hydrometallurgical processing of copper/cobalt oxide ores entails dissolving the ore with acid. The resulting acidic solution requires several steps to precipitate the dissolved element impurities from solution. Lime is used for various precipitation steps in these processes.

Nickel laterite hydrometallurgical processing

Hydrometallurgical processing of nickel laterites (limonites or saprolites) requires acidic conditions to dissolve the nickel within the laterite ore. This acidic solution is neutralized in several steps using lime, precipitating the dissolved element impurities from solution and recovering valuable base metals (Ni, Co, Cu) as precipitate products.

Silver recovery from sulfide refractory gold ores

During the pressure oxidation or autoclave processing of certain ore types, silver may deport to the residue as a co-precipitate in basic iron sulfates, preventing its recovery. A lime boil process can be used: at a high temperature silver-containing precipitates react with lime. This results in their conversion to iron oxides and/or hydroxides and the solubilization of silver for subsequent recovery.

Titanium oxide production

TiO₂ production from ilmenite FeTiO₃ makes use of sulfuric acid. Limestone and lime are required for neutralizing the resulting effluent and removing dissolved metal impurities prior to re-use or discharge into the environment.

Uranium yellowcake production

Sulfuric acid is used to leach uranium from certain ore types, often together with an oxidant such as ferric iron. Such leaching occurs either in situ, in heaps or in agitated tanks. After uranium recovery from solution (typically by solvent extraction) the residual, acidic solution bleed requires neutralization and treatment to remove the dissolved metals. Lime is used for both neutralization and precipitation.

Lithium production

Lithium, in the form of carbonate or hydroxide, is produced from several sources, including spodumene ore, lepidolite and brines. For these, the main drivers for lime consumption are:

Removing magnesium in brine recovery flowsheets
Neutralizing and removing impurities in spodumene flowsheets
Converting lithium carbonate to lithium hydroxide monohydrate

Safety & process applications

Moisture control in mineral solid products (transportable moisture limits)

Mineral products, such as iron ore and other mineral concentrates, need to comply with tightly-regulated transportable moisture limits that apply to bulk shipping. Too little moisture results in dusting problems. Too much produces fluidization of the material, with possibly disastrous consequences for bulk cargo ships. Lime CaO reacts with free water to form calcium hydroxide, thereby reducing the moisture content of the mineral products. Lime may also be used as a moisture control method for bulk mineral solids in climatic conditions that give rise to wet, sticky ores, causing problems during bulk handling.

Dewatering and flocculation of suspended mineral particles in thickeners

Lime can be used as a flocculant during thickening and settling of mineral particles, resulting in increased settling rates and improved dewatering during tailings disposal.

Hydraulic containment

Lime can modify the hydraulic properties of facilities for solution and tailings containment. Proviacal^® DD is a lime-based product specifically designed for hydraulic modification of dikes, dams and tailings facilities. www.proviacal.com

Mineral concentrate odor control

Odor control is important during storage, transport and handling of base metal, sulfide mineral concentrates. Flotation collectors, such as xanthates, are retained in mineral concentrates. Under certain circumstances, these organic compounds may decompose during the stockpiling, transport and handling of base metal concentrates. Decomposition products include gaseous organosulfur compounds that create significant odors. These could cause regulatory authorities to restrict the transportation of these concentrates. Using lime products in the final solid/liquid separation step of concentrate production can significantly reduce odors associated with mineral concentrates.

Coal-dust explosion prevention

Milled limestone is used in underground coal mining to prevent and suppress coal dust explosions. It is typically sprayed on mine walls, where it acts as a coal dust binder, preventing the dust from becoming airborne and contributing to the risk of explosion. In addition, bags of limestone are stored at strategic locations in the mine. In the event of an explosion they also explode. The resulting limestone dust dilutes the coal dust concentration, reducing its explosive impact and combustion potential.

Pyrometallurgical refining and smelting

Lime is used in a number of copper, nickel, aluminum and magnesium refining and smelting applications.

Copper and nickel

Fluxing agent in copper furnaces to create slag. Lime is stable at high temperatures and requires no energy input, unlike limestone, which removes energy that must be replaced.
Arsenic removal from copper in converters and anode furnaces, and for arsenic precipitation from roaster acid-recovery reject streams.
Scrubbing reagent to treat flux gases coming from base metal tapping operations.
Simplifying the filtration of captured dust, and helping prevent mud formation in bag filters that contain air moisture.

Aluminum

EMGESAL^® AI is a specialized aluminum fluxing and refining agent.

Magnesium

The EMGESAL^® FLUX range consists of high-quality, light metal fluxes tailored for magnesium refining. They remove non-metallic inclusions, provide melt protection and extinguish magnesium fires. Brochure Emgesal® - EN

Our Rheinkalk facility produces a range of non-lime, synthetic, anhydrous products based on carnallite (MgCl₂-KCl). These are available for smelting and refining light metals.

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Non-ferrous metallurgical processing