Non-Ferrous Mining and Metals

Non-Ferrous Mining and Metals

Minerals and lime products play a key role not only in the mining processes of non-ferrous metals, but also in treating resulting effluents in order to help protect the environment. They also help promote the safety of mine workers. We offer lime products of the appropriate purity and reactivity for optimal metal beneficiation. Our solutions have specific application in the refinement of copper, magnesium, zinc, nickel, uranium, gold, lead, niobium, cobalt and aluminum.

Ore beneficiation

Lime is an important part of the ore beneficiation processes for copper, aluminum, gold, nickel, zinc, cobalt, lead and other metals. Featuring the appropriate purity and reactivity, our lime products ensure the high efficiency required to reach elevated levels of metal beneficiation. Our solutions combine lime products and minerals with our proven expertise in the sustainable production of lime slurry, saving both energy and water.

Copper flotation

Lime slurry is added during milling operations and cell flotation to optimize copper recovery to:

  • provide the  alkaline conditions that enable the collector to make ore surface particles very hydrophobic, enabling their flotation. Optimal pH varies from 9 to 11 depending on collector type and pyrite content. Our lime products create these alkaline conditions in a cost-effective way.
  • depress the flotation of pyrite. A chemical reaction occurs during the grinding of lime and pyrite forming CaSO4 and Fe(OH)3. This makes pyrite surface particles very hydrophilic and inhibits their flotation. Lime optimizes the selectivity of copper recovery.

Bauxite-to-Alumina – The Bayer process

Lime slurry has the capacity to improve the digestion and filtration of bauxite-to-alumina. The Bayer process is the principal industrial means of refining bauxite to produce alumina (aluminum oxide).

Digestion

To produce sodium alumina liquor, bauxite ore is milled and slurried with caustic soda at a high temperature (140-240°C) using substantial pressure. Lime is added to capture phosphates and prevent them entering the alumina liquor. The insoluble residue (red mud), containing the inert materials and calcium-phosphates, is separated by clarification. Lime is also added to the separated red mud to react with the soluble Na2CO3, produced during the digestion stage, to recycle caustic soda (NaOH).

Filtration

The Na alumina liquor (overflow from the clarifier) is filtered to remove traces of fine mud. The addition of TCA (Tri-Ca-Aluminate) crystals helps this process. TCA is produced on site via a reaction between Na liquor and lime. Lhoist provides suitable lime products to create the right TCA particle size critical to filtration.

 

Gold production

Gold ore beneficiation is commonly conducted by cyanide leaching. Gold oxide ores are naturally disposed to cyanide leaching, while gold sulfide ores need pre-treatment (roasting, autoclave). Cyanide leaching can be carried out in either heap or agitated systems. In both systems, lime is added to either maintain or produce a pH>11 to prevent volatilization of the pregnant solution.

Cyanide heap leaching

 (preferred for low-grade gold <2 g/Ton ore)
Lime is added to the heap during construction. The cyanide solution is sprayed from the top of the heap to dissolve the gold. The resulting gold cyanide complex (pregnant solution) is extracted via the bottom of the heap and stored in ponds. We recommend also adding lime slurry to the pregnant solution in pond storage to ensure the required pH>11. If the pH is below 10.5, the risk of cyanide loss increases, raising operational costs and contamination.

Cyanide agitated leaching

 (preferred for high-grade gold >2 g/Ton ore)
The solution is transferred to carbon-in-pulp tanks where activated carbon adsorbs the gold, liberating the cyanide solution.

Lime consumption is substantial and depends mainly on the amount of cyanide present, as determined by the gold grade. Our lime products have the necessary reactivity to ensure high pH in a cost-effective way.

Niobium

This metal is obtained by pyrochlore concentration via the steps of wet grinding, magnetic-process separation, followed by flotation and refining. Lime is mainly used for phosphore removal.

The concentrate is first submitted to pelletizing and sintering process. Then the material enters an electric arc furnace, where lime is added in order to form slag and remove impurities from the bath. The metal obtained is purified and allows the commercialization of the following products: niobium oxide, special niobium oxide, standard grade ferroniobium, metallic niobium and masteralloys.

Nickel production and flotation

Lime is used in the flotation process of sulfide ores and in the acid leaching process of oxide nickel laterite ores in order to increase the concentration of nickel.

Lime acts in synergy with the collectors to depress impurities and achieve selective nickel flotation.

Acid leaching with sulfuric acid

Limestone and lime treat the acid pregnant solution in different steps:

  • Primary neutralization: limestone removes iron and aluminum.
  • Secondary neutralization: lime successively precipitates nickel and cobalt, the main products.
  • Final neutralization: lime removes heavy metals and manganese. Iron and Mn are waste materials. The final treated water is sent back to the chemical leaching step.

Metal refining: copper, magnesium and aluminum

Copper

Lime plays an important role in metal refining operations, such as in copper smelters.

It acts as a:

  • Flux agent in furnaces to create slag. Unlike limestone, lime is stable at high temperatures so requires no energy from the system. Limestone reacts with the heat to create calcium oxide, a process that removes energy which must then be replaced. Lime therefore offers greater benefits than limestone.
  • Reagent to treat flux gases coming from metal-tapping operations. Lime also simplifies the filtration of captured dust and helps prevent mud formation in bag filters with air moisture.
  • Reagent that removes arsenic from copper in converters and anode furnaces.
  • Reagent to neutralize acid wastewater before discharge into the environment.

Magnesium

Magnesium is an essential construction material used in a wide range of applications. A growing transport sector and energy saving requirements are driving the demand for this lightweight metal and encouraging improvements in its quality.

Rheinkalk HDW, a Lhoist subsidiary in Germany, has developed anhydrous high-quality fluxes under the brand name EMGESAL® FLUX for refining and enhancing the quality of magnesium.

These are used worldwide for:

Refining magnesium

Re-melting magnesium leads to non-metallic inclusions. Only ingots and class 1 scrap can be re-melted without the use of flux. EMGESAL® FLUX collects all non-metallic inclusions from the magnesium melt and separates them from the clean metal.

Protecting molten magnesium

EMGESAL® FLUX provides additional benefits to the covering and protection of gas, including covering flux. It is recommended:

  • for furnaces without continuous gas protection
  • as a reserve in case of disturbances in the gas supply
  • as an alternative vs. environmental unfriendly Greenhouse gases like SF6 or SO2.
Extinguishing magnesium fire

EMGESAL® FLUX is the most efficient fire extinguisher for magnesium. It forms a molten layer on top of the liquid magnesium to exclude oxygen. As a synthetic Carnalite, it complies with the ternary eutectic in MgCl2-KCl-NaCl-System. Sufficient amounts of dry salt flux should always be on hand; well-marked flux bins should be located at work stations and in machine areas where liquid magnesium is present.

Anhydrous • homogeneous • dust free
  • Anhydrous EMGESAL® FLUX can be used without any hazardous environmental emissions during the magnesium melt.
  • Homogeneous EMGESAL® FLUX forms a liquid flux layer protecting the molten magnesium against oxidation. Burning magnesium is avoided. Metal losses are minimized.
  • Flake-formed and dust-free EMGESAL® FLUX prevents dust emissions and ensures rapid protection and safe advanced performance.

Brochure Emgesal®

Aluminum

As a lightweight metal, aluminum is widely used in the construction industry. Users require ever-higher quality standards, which added to a growing transportation sector and energy saving requirements means demand is increasing.

REFINAL® Aluminum Fluxes were developed in cooperation with partner MQP, a provider of innovative technologies and equipment for the aluminum industry.

http://www.mqpltd.com/

Dilution of rock dust

Milled limestone is used in underground coal mining to prevent and suppress explosions. Sprayed on mine walls, it inhibits the loosening of fine coal dust that could become airborne and create an explosive fuel. Bags of limestone are stored in strategic locations so that, in the event of an explosion, the limestone will float in the air and dilute the concentration of coal dust. This limits the spread of combustion. Low silica levels and closely-controlled gradation are important for optimum product performance and to promote the safety of coal mine workers.

Environmental processes

Ore beneficiation produces acidic wastewater. Metal refining also produces acidic wastewater as well as flue gas. Effluents contain both acid and heavy metal pollutants that must be removed in order to meet strict low emission levels before they are discharged into the environment. We have developed specific lime products, Neutralac® and Sorbacal®, for wastewater treatment and flue gas cleaning systems to help you meet emission requirements in a cost-effective way.

Preventing and treating Acid Mine Drainage (AMD)

AMD facilitates the treatment of pyrite from excavated overburden that has been oxidized by air and water. Mixing limestone reagents to the overburden ensures that the neutralizing effect happens precisely where the acid has been created. Limestone is used to prevent leaching of heavy metals into the groundwater.

www.neutralac.com

Acidic lake neutralization

During the extraction of minerals, other minerals may also be brought to the surface. These can cause acidic loading that may lower the pH in rivers and lakes. Acid waters release heavy metals previously bound in the soil that endanger the quality of groundwater and drinking water. Rising surface water also leads to acidification of connecting lakes and rivers. This is true for most post-mining lakes. To save potentially important bodies of water from ecological harm and turn them into areas suitable for touristic use, they must be sustainably renaturalized.

Lhoist has 20 years of experience in the neutralization of acidic lakes using specially developed boats. We tailor our Neutralac® reagents to meet the precise requirements of individual applications, supported by rigorous university research.

Treating mining effluents

For more than 50 years, uranium was extracted from mines in Eastern Germany and the Czech Republic. This was achieved via leaching using sulfuric acid, nitric acid and ammonia. The result was extremely acidified rocks comprising sulfuric acid, heavy metals and radioactive elements that endangered groundwater. Neutralac® Q solves such issues. It allows you to effectively treat acidification and prevent the leaching of heavy metals.

We can provide:

  • laboratory tests on the quality of milk of lime, quicklime and water
  • long-term trials using our mixing installation Duwa-Matic® 650 along with Neutralac® Q
  • engineering of Duwa-Matic® technology with the capacity of 2x3.2 t/h Neutralac® Q.

Lhoist offers a wide range of Neutralac® and Sorbacal® reagents and technologies which are complemented by our expertise. We are also constantly working to develop new solutions.