Abstract: Depositional formula of heavy metals after disposal of the mine drainage from the Ogoya Mine in Ishikawa Prefecture, Japan, was mineralogically investigated. Strong acidic wastewater (pH 3.5) from pithead of the mine contains high concentration of heavy metals. In this mine, neutralizing coagulation treatment is going on by slaked lime (calcium hydroxides: Ca(OH) (sub 2) ). Core samples were collected at disposal pond to which the treated wastewater flows. The core samples were divided into 44 layers based on the color variation. The mineralogical and chemical compositions of each layer were analyzed by an X-ray powder diffractometer (XRD), an energy dispersive X-ray fluorescence analyzer (ED-XRF) and a NCS elemental analyzer. The upper parts are rich in brown colored layers, whereas discolored are the deeper parts. The color variation is relevant to Fe concentration. Brown colored core sections are composed of abundant hydrous ferric oxides with heavy metals, such as Cu, Zn, and Cd. On the other hand, S concentration gradually increases with depth. XRD data indicated that calcite decreases with increasing depth, and ettringite is produced at the deeper parts. Cd concentration shows similar vertical profile to those of calcite and ettringite. The results revealed that hydrous ferric oxides, calcite and ettringite are formed on deposition, whereby incorporating the heavy metals.

Abstract: Surface waters in the Pine Creek Geosyncline (located in Australia's “Top End”, defined as the area of Australia north of 15 degrees S) are characterized by their low carbonate buffering capacity. These waters are buffered by silicate weathering and hence are slightly acidic, ranging in pH from 4.0 to 6.0. The Pine Creek Geosyncline contains most of the Top Ends' economic mineral deposits and characteristically shows no correlation between carbonate minerals and sulfidic orebodies hosting gold deposits (unlike uranium deposits). Thus many gold mines do not have ready access to carbonate minerals for buffering acid mine drainage (AMD). It is possible that locally available fast-weathering silicate minerals may be used to buffer AMD seeps. The buffering intensity of silicate minerals exceeds that of carbonate minerals, but their slow dissolution kinetics has ensured that these materials have received little attention in treating AMD. In addition, carbonate mineral dissolution is retarded when contacted with intense AMD solutions due to the formation of surface coatings of iron minerals. The lower pH range of silicate mineral dissolution may prevent the formation of such coatings. The Pine Creek Geosyncline consists of a complex geochemistry, and a number of fast-weathering silicate minerals have been noted in various areas. The difficulty in assessing such minerals for use in buffering AMD is the lack of kinetic data available under conditions prevalent AMD (i.e., low pH solutions saturated with aluminium and silica). This study sets out to evaluate the applicability of using such minerals to treat AMD surface seeps.

Abstract: Agricultural soils irrigated with acidic mine water from the Guangdong Dabaoshan Mine, China, were investigated. The pH of the soils could be as low as 3.9. However, most of the mineral acids introduced into the soils by irrigation were transformed to insoluble forms through acid buffering processes and thus temporarily stored in the soils. Different heavy metals exhibited different fraction distribution patterns, with Zn and Cu being mainly associated with organic matter and Pb being primarily bound to oxides (statistically significant at P = 0.05). Although the mean of exchangeable Cd was greatest among the Cd fractions, there was no statistically significant difference between the exchangeable Cd and the oxide-bound Cd (the 2nd greatest fraction) or between the exchangeable Cd and the carbonate-bound Cd (the 3rd greatest fraction). It was also found that there were generally good relationships between the concentrations of various Zn, Cu, Pb, and Cd fractions and pH, suggesting that a major proportion of each heavy metal in the soils was mainly derived from the acidic irrigation water. The results also show that the crops grown in these soils were highly contaminated by heavy metals, particularly Cd. The concentration of Cd in the edible portions of most crops was far in excess of the limits set in China National Standards for Vegetables and Fruits and this can be attributable to the extremely high transfer rate of Cd from the soils to the crops under the cropping system adopted in the study area. < copyright > CSIRO 2005.