Proposed Limpopo West Mine Concept Study ... - SRK Consulting

SRK Consulting: 447493: Limpopo West Geochem Page 28Contact LeachVarious forms of contact leach test are used to simulate the pore water composition that will seepfrom residues stockpiles. In the mining industry the Synthetic Precipitation Leaching Procedure(SPLP) at pH 4.2 and solid: liquid ratio 1:20 has been widely used where acid rain is prevalent orwhere the residues are considered to be acid producing. Contact leach tests have been widely usedby many recent investigators as opposed to SPLP due to the following reasons:The SPLP leach using the specified 1:20 solid: liquid ratio is likely to over-dilute the simulatedpore water in all but the wettest areas, leading to under-estimation of contaminantconcentrations;The pH 4.2 used commonly in the SPLP procedure may be more aggressive in most cases thanwould be experienced in the field, leading to over-estimation of certain contaminants;Distilled/deionized water extract at a higher solid: liquid ratio than 1:20 is considered to provide amore pore water quality result.The distilled water shake flask test (ASTM D3987) was used to leach raw material samples. Thesamples were shaken for 24 hours at a solid to liquid ratio of 1:10. A summary of the distilled waterleach test are presented in Appendix B.The results indicated that the leachate ranged from slightly acidic to alkaline (pH 5.0 to 8.6). Themajor constituents that contribute to salinity include Ca, Mg, Na, K and SO 4. Sulphate had thehighest concentration (58 to 6 640 mg/l) in the leachate of all samples, with 50% of the samplesexceeding the SANS 241:2011 guidelines.GOGP/LAKJ Report_April2013_19April2013 (1)_Final_Ludi_22052013 April 2013