The effect of kimberlite weathering on the behaviour of waste material at Cullinan diamond mine, South Africa / Jessica Strydom

• Main Author: Strydom, Jessica
• Language: en
• Published: 2015
• Subjects: Cullinan kimberlite; Kimberlite weathering; Cullinan No 7 Dam; Clay mineral; Suspension; Dispersion; Coagulation; Flocculation; Wastewater quality; High humidity leaching; Zeta potential
• Online Access: http://hdl.handle.net/10394/15586

Water quality and space constraints have become major concerns regarding the No. 7 waste water dam at Petra Diamonds’ Cullinan mine. The unique location of the dam constrains further development, while unsustainable accumulation of waste water inside the dam increases the risk of potential environmental contamination from seepages and spillages. The dam retains a significant amount of very poor quality water. Its excessively high pH, dissolved salt content, density and extreme turbidity result from the concentration of natural weathering products of the diamond bearing kimberlite ore. The turbidity results from the dispersion of colloidal chlorite, saponite and nontronite clay. Along with the chemistry of the solution, their colloidal shape contributes equally significantly to the non-settlement of these suspended clays. Flocculation of the dispersed clay particles will provide (a) for easy and effective separation of the clay material from the waste water and (b) more convenient options for water treatment (and subsequent redistribution) This study was aimed at contributing to a better understanding of the dynamic interactions in the No 7 Dam system to contribute towards identifying a suitable means/method for chemical flocculation of the clay particles. The individual components of the system (clays, water quality) and influx contributors (kimberlite and its leachate) were systematically characterized by means of X-Ray Diffraction, X-Ray Fluorescence, petrographic microscopy, electron microscopy, electrophoretic mobility and standard water- and soil quality analyses. The baseline quality of the Cullinan kimberlite leachate was obtained based on ASTM D5744 principles. It was found that adjusting the pH-level and ionic strength of the waste water to the critical coagulation point (cK) (as determined by electrophoretic mobility and batch jar experiments) automatically induced coagulation. Higher valence cations were displaced from pH dependent surface charge sites by proton adsorption. The resultant increased ionic strength, in combination with decreased thickness of the ionic double layer, was sufficient for the automatic initiation of high strength disordered face-face and edge-face bonds. During batch Jar tests, flocculation initiated within 4 minutes after the addition of HCl (0.5 M) and total sedimentation completed within 3 hours. The use of commercial flocculants might decrease the sedimentation time. As expected a significant increase in dissolved salt content of the clear supernatant was observed. No re-dispersion of the dried clay occurred. Throughout the study geochemical modeling was performed with PHREEQC software to identify/determine possible effective experimental conditions, minimizing experimental time and expenses. The program was also used to model outcomes of the possible water treatment options, indicated in literature as viable options for similar situations. These options can be tested to extend upon the current research. === MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015