Jarosite KFe3+3(OH)6(SO4)

Jarosite is a secondary iron sulphate often found in acid mine drainage environments, particularly in mining wastes from polymetallic sulphide ore deposits. Despite the negative environmental connotation usually ascribed to secondary sulphate minerals due to the release of hazardous elements to aquifers and soils, jarosite acts as an efficient remover and immobilizer of such metals, particularly lead. Jarosite precipitation is used in hydrometallurgy, especially the zinc industry, to control iron, sulfate, and other impurities.

Pollution Problem Associated with Jarosite

During metallic zinc extraction from zinc sulphide or sulphide ore, a huge quantity of jarosite is being released universally as solid residues. The jarosite mainly contains iron, sulphur, zinc, calcium, lead, cadmium and aluminium. Jarosite released from such industrial process is complex and its quality and quantity make the task more complex for safe disposal. Apart from water contamination, jarosite already accumulated and its increasing annual production is a major source of pollution for surrounding environment including soil, vegetation and aquatic life and hence its disposal leads to major concern because of the stringent environmental protection regulation.

Jarosite applications with Ferrate(VI)

Ferrate can be mixed with other ingredients as mixtures or solid solutions with which it is compatible when used alone or as a Part A in a multiple part system; for example, to provide ease of use and/or to effect faster, more efficient, and/or more complete whitening, bleaching, sterilization, and/or cleaning properties. One preferred formulation includes solid solutions of ferrate(VI) ion by ion substitution to form carrier salt materials, preferably with sulfate ion materials, such as with potassium sulfate, calcium sulfate, magnesium sulfate, sodium sulfate, aluminum sulfate, and zinc sulfate, including the basic (hydroxide ion-containing) forms, and/or chromate(VI) forms, for example, Jarosite.

Other solid solutions of sulfate may include solutions comprising sodium ion, lithium-ion, potassium ion, or other alkali metal ions or alkaline earth ions. Especially preferred formulated materials are anhydrous potassium sulfate and/or anhydrous calcium sulfate solid solutions of ferrate(VI) ion. In these above “solid solution” compositions of matter, the carrier salt or mineral contains ferrate(VI) ions to the mole fraction of ferrate/sulfate ion, is preferably from 1 to 100%, more preferably 2-10%.

Ferrate(VI) solution of jarosite structure, i.e. [KFe3(FeVIO4)2(OH)6] as an essentially pure compound or fraction of potassium jarosite material. This new composition also pertains to other jarosites too, such as where K+ is replaced in whole or in part by Na+, AgI, NH4+, Tl+, Li+, and the like, where again Roman numeral subscripts refer to formal oxidation states on the metal ion, while +’s and −’s refer to electric charges on the ions.

Jarosite wastes generated from the hydrometallurgical process contain a significant quantity of compounds of iron, zinc, sulphur, lead, cadmium, manganese, etc. The presence of toxic substances make these wastes hazardous and possess serious problem for their disposal. However, due to weathering/bacterial action, there is a release of toxic elements in a soluble form which ultimately contaminates the soil, groundwater, and aquatic life due to improper management of such hazardous wastes.

To conclude there are two ways of beneficial usage of sodium ferrate concerning jarosite:

  • Combination of sodium ferrate with jarosite to increase the efficiency of the treatment process. This will help to maintain the problem of the utilization of jarosite waste;
  • Treatment of toxic elements from the soil, groundwater, and aquatic life with sodium ferrate during metallic zinc extraction from zinc sulfide or sulfide ore.

Zinc mines in Finland: yellow - smelter, green - operating, red - discontinued