An accelerated kinetic leach test for geochemical and environmental characterisation of acid and metalliferous drainage

Description

This study developed a new accelerated kinetic tests to assess the acid and metalliferous drainage (AMD) potential of six legacy mine waste samples from Tasmania, Australia. The new test seeks to eliminate the uncertainty associated with geochemical static tests and provide a shorter and cheaper alternative to conventional kinetic tests that is applicable to a large number of samples onsite or in a laboratory. The dataset is as follows: 1. Particle size distribution of crushed Spray, Dundas, Site X, Endurance and Mt Lyell mine waste samples and "as received" Zeehan smelter tailings. 2. Mineralogy per size fraction for Spray, Dundas, Zeehan smelter, Site X, Endurance and Mt Lyell mine waste samples. The mineralogy was used to evaluate the theoretical AMD potential of the mine waste samples, which was compared to the acid-base accounting results. 3. pH and electrical conductivity profiles of leachates generated by Spray, Dundas, Zeehan smelter, Site X, Endurance and Mt Lyell mine waste samples over 100 days. The profiles show the lag phase and onset of acid-generation after day 10. 4. Chemistry of leachates generated by Spray, Dundas, Zeehan smelter, Site X, Endurance and Mt Lyell mine waste samples on days 1, 5, 10, 26, 50 and 100. Some PTEs including Al, As, Cr, Cd, Pb, and Zn exceeded the environmentally acceptable concentrations specified for freshwater in Australia, thus the mine waste samples pose moderate to extreme risk based on water hazard indices.

Steps to reproduce

1. The composite samples ( about 80 kg) were collected by bucket and shovel at least 0.5 m below the exposed surface of mine waste piles. The samples were oven-dried at 40 degrees Celsius and split by cone and quartering. After crushing to below 4 mm, the samples were split by a rotary splitter. Two selected splits were dry sieved to determine the particle size distribution. 2. The mineralogy abundances of each size fraction were quantified by an FEI mineral liberation analyser (MLA) Quanta 650 scanning electron microscope equipped with a Bruker Quantax Esprit energy-dispersive X-ray spectrometry (EDS) system and twin Xflash 5030 silicon drift detectors. Analyses were conducted on representative areas of the polished one-inch epoxy resin grain mounts coated with 20 nm carbon. The instrument was operated at 20 kV accelerating voltage and 7nA beam current. Mineral identification and quantification were performed using the advanced mineral identification and characterisation system (AMICS) software. 3. The accelerated kinetic test was conducted on 14 g of milled (below 75 micron) sample leached with 30 mL of deionised water in 35 mm diameter porcelain Buchner funnels. The wetting cycle was followed by drying at 35 degrees Celsius with heat-lamps for 2 days. After 1 month the drying period was increased to 10 days until 100 days had elapsed. pH and EC of the generated leachates were measured after every wetting-cycle. The leachate chemistry was analysed on days 1, 5, 10, 26, 50 and 100 using a Thermo Scientific iCAP 7400 ICP-AES.

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