Witwatersrand Basin_Mineral and Trace Elements Data

Published: 25 November 2021| Version 1 | DOI: 10.17632/wxw27gz8rj.1
Contributors:
Lowanika Victor Tibane,

Description

The Witwatersrand basin in South Africa comprises unrehabilitated mining waste tailings characterised by unbalanced content of trace elements including Fe, S, Cu, Mn, Cr(t), Zn, Ni, Co, Mo, and P. To assess the quality of soil from the abandoned historical gold mine tailings, the geochemical, pH, and electrical conductivity data were generated from 21 soil samples. The data show a significantly low pH ranging from 1.9 to 5.3 and electrical conductivity ranging from 43 to 679 mS/m. A concentration factor expressed as the ratio of the concentration of trace metals in the samples to the concentration of trace metals in the background soil, used together with geoaccumulation index (Igeo) show that the investigated sites comprise elevated Cu content in the tailings than in the uncontaminated crustal background soil.

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1. Lithological sampling 1.1. Collect conglomerate samples for petrographic descriptions at hand specimen scale and use polished thin sections under ore microscope for mineralogical and textural data. 1.2. Prepare X-ray diffraction (XRD) data using a back-loading preparation method and a PANalytical X’Pert Pro powder diffractometer with X’Celerator detector and variable divergence and receiving slits with Fe filtered Co-Kα radiation. Identify phases using X’Pert Highscore plus software and quantify the phasse in weight percentage (wt%) using the Rietveld Autoquan Program and report errors on 3 sigma level. Amorphous phases, if present, were not considered. 1.3. Prepare X-ray flourescence (XRF) data using samples milled to <75 µm in a Tungsten Carbide milling vessel, roasted at 1000 ºC to determine Loss On Ignition (L.O.I). Add 1g sample to 9g Li2B4O7 fused into a glass bead and use ARL9400XP+ spectrometer to generate major element data. Use an aliquot of the sample pressed in a powder briquette for trace element data. 2. Soil sampling 2.1. Record coordinates the exact sampling location using mobile smartphone equipped with global positioning system. 2.2. Collect two soil samples at each tailing location, the first sample from upstream and the second sample from downstream. 2.3. Remove the top 30 cm using a shovel, collect 500 g of soil at obvious soil contacts between 30 cm 150 cm depth. 2.4. Use hand gloves, and wash the sampling tools using distilled water after each sampling point to avoid contamination from previous samples. 2.5. Place the samples in amber brown glass bottle containers and transport the bottles to the laboratory in a cool box within a period of 24 hours for generating trace element data using ICPEOS method. 2.6. Utilise the inductively coupled plasma-mass spectrometry (ICP-MS) to produce trace elements data under 1300 W RF power, 15 L/min plasma flow, 2.0L/min auxiliary flow, 0.8 L/min nebulizer flow,1.5 L/min for sample uptake rate. Digested a portion of the sample using dilute aqua regia and then analyse the digest or recoverable Hg by ICP-MS. 2.7. Graphs and tables are created using Microsoft Office Excel, Version 16.16.27 (201012). 2.8. Calculate the Contamination Factor (CF) = (Cm)/(Cb), expressed as the ratio of the metal concentration in the sample to the metal concentration in the uncontaminated soil. Cm is the measured metal concentration in the samples, whereas Cb represents the background concentration of the metal in unpolluted soil obtained as the average crustal concentration. 2.9. Determine the geoaccumulation index (Igeo) = log2(Cn/1:5 Bn). Cn metal concentration in the investigated sample. Bn is the background concentration of the metal as determined from the global shale concentration. The value of 1.5 is a constant that accounts for the lithogenic variations in the background concentration for a particular metal in the environment.

Institutions

University of KwaZulu-Natal

Categories

Environmental Science, Soil Geochemistry, Soil Mineralogy

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