Influence of natural fulvic acid on solubility of sulfide ores (experimental investigation)

Novikova S.P.

V.S. Sobolev Institute of Geology and Mineralogy sb ras, Novosibirsk, Russia

sveta.novikova@gmail.com

Nowadays a great attention is paid to the problems of the functioning of the anthropogenically disturbed ecosystems of the ore regions and particularly to the factors determining the scope and ways of toxic heavy metal migration [1]. It is widely known that the element behavior in the drainage waters, sediments and soils is regulated by Eh-pH conditions of the environment along with the presence of natural humic substances. Their most important property is the ability to form soluble and insoluble complexes with metal cations depending on the composition (fulvic and humic acids, humin) and concentration and thus promoting or inhibiting leaching of the ore material or the accumulation of secondary phases [2].

This research is an experimental study of the oxidation process of pyrite-polymetallic ores under presence of fulvic acids (low molecular weight fraction of humic substances) in solutions with variable acidity. As an initial solid material the ore from the Kyzyl-Tashtyg deposit (Tuva Region, Russia) was chosen. The material is of a high interest due to planned exploit of the deposit [3]. New data on a possible chemical composition of acid mine drainage can be especially relevant and practically useful.

Fig. The sample fragment of the oxidized ore. 1, 3 - chalcopyrite, 2 – Fe oxide, 4 - pyrite.

Model experiments were performed to study the solubility of sulfide ores in a distilled water and in the solutions with different fulvic acid (FA) content. Experimental solutions were obtained from the peat (Kirsanovskoe swamp, Tomsk region, Russia). It was determined that under atmospheric conditions the sulfide mineral oxidation gives presumably a rise to a formation of an acidic drainage containing toxic heavy metals (Cu, Zn, Cd). The impact of a natural FA depends on the ability of the ore solid material to neutralize the acidity of the solution. If the quantity of carbonates is sufficient at the first stage of oxidation, a significant increase in pH of the solutions without the FA ensures Fe and Cu removal into the solid phase (Fig.). Metal precipitation can be prevented by the formation of soluble fulvic-metal complexes under relatively more neutral and alkaline pH conditions. However, at a later stage, when there is an exhaustion of the neutralizing capacity of rocks, all solutions remained acidic for more than 100 days of leaching process. In this case FA inhibited the oxidation of sulfide minerals from the surface and reduced the removal of heavy metals into the solution.

Cu tended to precipitate on the surface of humic acids (high molecular weight fraction of humic substances) and this trend was intensified with increase of copper containing solution initial pH value.

References:

1. Bortnikova S.B., Gaskova O.L., Bessonova E.P. (2006) Geochemistry of anthropogenic systems, 168pp.

2. Kabata-Pendias A. (2001) Trace elements in soils and plants (3rd ed.) CRC Press LLC, 331pp.

3. fedpress.ru/federal/econom/news_kompany/id_166522.html