Danie Vermeulen

Geochemical Modeling and Remediation of Heavy Metals and Trace Elements from Artisanal Mines Discharge

ABSTRACT Geochemical modeling of heavy metals released from the activities of artisanal mining for gold exploitation was investigated in this study. Samples of mine water and sediment discharges were collected before and after treatment. Untreated discharge shows pollutant of arsenic, lead, cadmium and iron in water and sediment above the acceptable standard. Manganese was above detection limit in the treated water discharge after treatment. Aqueous modeling in solution and solid-state reaction showed over-saturated indices for tenorite, bixbyite, cupric ferrite, cerrusite and manganite in the untreated mines discharge and hausmannite, ferrihydrite and goethite after treatment.The identified toxic metals were absent or had low contamination factor in the mines discharge water after treatment. The study highlights the danger posed by artisanal mining to the environment and suggests treatment method.

Aquifer vulnerability assessment of the Dahomey Basin using the RTt method

This paper presents the theory and application of rainfall and travel time (RTt) vulnerability method. The method is applied on a shallow aquifer in the Dahomey Basin of south-western Nigeria with the results being compared to other established vulnerability assessment methods. The method follows the source pathway receptor concept of aquifer vulnerability assessment where rainfall represents the driving force for the downward percolation of contaminant to the water table while travel time represents ease of contaminant movement to groundwater. The travel time is derived from the depth to water table and infiltration rate in the vadose zone. Aquifer vulnerability maps were produced by interpolation techniques using the direct weight method. RTt vulnerability data were rated into five classes and assigned equal values ranging from 12 to 100. These classes and ranges include: 12–29 very low, 29–47 low, 47–65 moderate, 65–83 high and 83–100 very high vulnerability. The resultant RTt vulnerability map was compared with the established DRASTIC, PI and aquifer vulnerability index (AVI) vulnerability assessment methods. The AVI shows high vulnerability throughout the study areas while DRASTIC ranged between low, moderate and high vulnerability similar to the RTt method. The low to moderate vulnerability was areas receiving low rainfall and higher vadose thickness. RTt vulnerability comparison with these methods and its validation show the advantages of RTt method in assessing aquifer vulnerability with a few critical parameters, particularly for the assessment of shallow resource aquifers in data-lacking areas.

Intrinsic vulnerability assessment of shallow aquifers of the sedimentary basin of southwestern Nigeria

The shallow groundwater of the multi-layered sedimentary basin aquifer of southwestern Nigeria was assessed based on its intrinsic vulnerability property. The vulnerability evaluation involves determining the protective cover and infiltration condition of the unsaturated zone in the basin. This was achieved using the PI (P stands for protective cover effectiveness of the overlying lithology and I indicates the degree of infiltration bypass) vulnerability method of the European vulnerability approach. The PI method specifically measures the protection cover and the degree to which the protective cover is bypassed. Intrinsic parameters assessed were the subsoil, lithology, topsoil, recharge and fracturing for the protective cover. The saturated hydraulic conductivity of topsoil, infiltration processes and the lateral surface and subsurface flow were evaluated for the infiltration bypassed. The results show moderate to very low vulnerability areas. Low vulnerability areas were characterised by lithology with massive sandstone and limestone, subsoils of sandy loam texture, high slopes and high depth to water table. The moderate vulnerability areas were characterised by high rainfall and high recharge, low water table, unconsolidated sandstones and alluvium lithology. The intrinsic vulnerability properties shown in vulnerability maps will be a useful tool in planning and monitoring land use activities that can be of impact in groundwater pollution.

Investigation of the Metal Contamination in the Upper Olifants Primary Catchment by Using Stream Sediment Geochemistry, Witbank Coalfield, South Africa

The Olifants primary catchment area, consists of nine sub-catchments marked from B1 to B9, extends over the border between South Africa and Mozambique, and has a total area of approximately 87,000 km2. The B1 catchment, where most of the mining activities surround the major towns of Witbank (Emalahleni) and Middleburg, in turn straddles the provinces of Mpumalanga and Limpopo. Although industrial and agricultural activities are also important, the contribution of contamination from the mining activities within the catchment is significant as the result of intense mining activities of various mineral commodities such as coal and from ferrochrome processing plants located in Emalahleni and Middleburg towns with in the catchment area and yet not fully quantified. This paper investigates the severity of the mining impacts on the water resources and the ecosystem of the Olifants primary catchment area and in particular, the upper reaches of the catchment. The paper discusses the results of research which focused on deciphering the severity and the sources water contamination, and on how to minimise the dispersion of these metals into the streams, and on the relationship of the water quality and metal loadings on the sediments. Stream sediment and water samples have been collected and analysed. The sediments were analysed by Simultaneous X-ray Fluorescence and Inductively Coupled Plasma-Mass Spectrometry techniques for metal loadings. The areas were marked by anomalous level determined at 50th percentile threshold of Fe, Mn, Ni, Cr, Co, V, Pb in Emalahleni and Al, Fe, Mn, Cr, As, Zn, Pb and U in Middleburg. The ICP-MS and IC analytical techniques were used in the assessment of water quality data. From the stream sediments regional geochemistry at catchment level and for this investigation, the sediments that were found marked by high levels of Na, K, Mg, Al, Ca, Mn, and Fe signature can be attributed to the coal mines as a probable source. Whereas the sediment quality of the areas like Emalahleni and Middleburg towns, where mining of coal (with many abandoned mines) and ferrochrome processing is happening simultaneously, there are anomalous level of Cr, Ni, V and As, which is a signature of the Bushveld PGE mines material. The SO4 2− concentration of above 500 mg/kg on the water quality, which has exceeded the Department of Water Affairs water quality guideline for domestic and industrial use, is an evidence for contamination. The approach adopted herein suggests that the stream sediment and water quality data can be used in characterizing or fingerprinting impacted areas.