Biological Influence on the Mobility of Metals from Mine Tailing Dump Located in Krugersdorp Area

Anthropogenic activities such as mining and smelting of metals ores have increased the prevalence of heavy metals which mobility in the tailing dumps or solid wastes is increased following deposition of the later in the environment. In nature, microbes are involved in weathering of rocks, in the mobilization of metals from minerals, in the reduction and oxidation of metals, and in metal precipitation and deposition. A six steps sequential extraction method, according to the Tessier method was used to fractionate heavy metals into the following fractions (F1) water soluble fraction (H2O), (F2) exchangeable metals, (F3) easily reducible fraction (CO3), (F4) Moderately reducible fraction (Oxide), (F5) metals associated with organic matter and secondary sulphides (organics) and (F6) a residual fraction. The results showed higher concentrations of heavy metals such as Fe, Pb and Zn, which were dominant in various fractions of the different sampling points (top, middle and bottom of the tailing dump). The DNA sequencing was carried out on tailing samples to identify the microorganisms likely to promote the mobility of metals. Among the host of microorganisms identified, autotrophic species such as Leptospirrillum sp and Sulfobacillus, as well as heterotrophic species such as Bacillus sp and Pseudomonas sp are those frequently reported in bioleaching processes. The binding groups identified by FTIR attest of the presence of organic matters which are likely to be involved in the entrapment of metals in the organic fraction of the tailing dumps. With most of the metals being attached to the exchangeable and the organic fractions of the tailing dumps, coupled with the presence of active microorganisms, the susceptibility of metal release from the tailings is more probable overtime.