Mining and Metal Pollution: Assessment of Water Quality in the Tarkwa Mining Area

The quality of water in mining communities is uncertain since metals associated with acid mine drainage are known to saturate these waters. Previous studies in Tarkwa, an area noted for gold and manganese extraction, have reported large concentrations of aluminium, arsenic, cadmium, copper, lead, manganese and mercury in water samples. This research aimed at investigating the chemistry of groundwater with special focus on the contamination status of trace elements. It also compared levels of metal concentration with those that were determined in previous research works, to identify changes that might have occurred. Thirty-eight water samples from boreholes, hand-dug wells and streams, within the Tarkwa area were obtained and analysed. Results show that 90 % of water in the area is acidic and Eh was determined to be positive, depicting oxidizing conditions. Mean groundwater temperature was 28.9 ºC. Thirty-two samples had either temperature or pH values falling outside the range recommended by the World Health Organisation (WHO). Thirty samples had at least one metal concentration exceeding the WHO guideline values. Among the list of elements that exceeded the guideline, arsenic, manganese, nitrate, nitrite and iron were the most predominant. The dominant ions in the samples were sodium and bicarbonate. High concentrations of Fe and SO42- in some parts of the study area point to the influence of acid mine drainage (AMD). Comparisons of results of metal concentrations with findings from previous research in the area showed a reduction in concentration. Hydrochemical modelling with PhreeqC attributed this reduction to sorption processes. Comparison of levels of metal concentration in the different water supply facilities (borehole, hand-dug well and stream) showed no significant variations. Keywords: Water Quality, Drinking Water, Hydrochemical Modelling, Heavy Metals

Statistical approaches and hydrochemical modelling of groundwater system in a small tropical island

The aquifer of Manukan Island of Borneo, Malaysia had been found to be affected by seawater intrusion associated with excessive groundwater exploitation. This research attempted to characterize the chemistry of an impacted zone in the island using factor analysis (FA), cluster analysis (CA) and a hydrochemical model package (PHREEQC). The factor scores were used to plot the spatial map and to group the relationships among the monitoring wells using CA. The results of FA analysis revealed that the three main processes associated with the seawater intrusion event are aquifer salinization, cation exchange process and redox sequences. Output from the PHREEQC simulation was used to support the findings from the multivariate analysis.

Solubility of mimetite Pb5(AsO4)3Cl at 5 - 55°C

Environmetal context.The mobility of toxic arsenic compounds in the environment can be controlled by the solubility of certain minerals. To predict and model the fate and behaviour of these contaminants, the solubility and related thermodynamic properties of the lead and arsenic mineral mimetite were determined. The data obtained in this study will be used to optimise and increase the effectiveness of remediation procedures that are already applied to contaminated sites. Abstract.The solubility of the synthesised mimetite was measured in a series of dissolution experiments at 5–55°C and at pH values between 2.00 and 2.75. The solubility product logKSP for the reaction Pb5(AsO4)3Cl ↔ 5Pb2+ + 3AsO43– + Cl– at 25°C is –76.35 ± 1.01. The free energy of formation ΔGf,2980 calculated from this measured solubility product equals –2634.3 ± 5.9 kJ mol–1. The temperature dependence of the logKSP is non-linear, indicating that the enthalpy of the reaction depends on the temperature. The enthalpy of the formation of mimetite ΔHf0, is –2965.9 ± 4.7 kJ mol–1, the entropy, ΔS0, is 39.5 J mol–1 K–1, and the heat capacity, ΔCp,f0 is –6172 ± 105 J mol–1 K–1. Hydrochemical modelling indicates that regardless of the composition of the background solution, Pb5(AsO4)3Cl is most stable at neutral to weakly alkaline pH.