Abstract: Lime neutralization is a frequently used method in the mining industry for the treatment of acid waters. These waters contain metal ions such as zinc, manganese, copper, cadmium, lead, etc. The conventional, straight lime neutralization technology generates a Low Density Sludge (LDS) having only 1-2% solids content. This creates sludge disposal difficulties, and results in the loss of potentially large quantities of recovered water, which in turn increases the demand for fresh water requirements for mining/milling activities. The High Density Sludge (HDS) process, on the other hand, is the state-of-the-art technology in North America. It generates a dense sludge with less volume and better particulate properties. Furthermore, the typical gelatinous nature of the sludge changes to a granulated, sand-like texture. Boliden Apirsa, S.L. investigated the feasibility of an HDS process to increase the treatment capacity of their existing plant, and resolve the issues associated with the LDS process for their Los Frailes project. The project required, given that the production of ore was going to be doubled, a significant increase in water was needed without altering the water reservoir sitting north of the concentrator. In addition, the final effluent quality was a priority issue. First, a pilot-scale study was undertaken in 1996, and parameters critical to the design and performance of the process were determined. The results showed that the HDS process could significantly improve the sludge characteristics by increasing the solids fraction from 1.5 to 12.0%, thereby decreasing the sludge volume to be disposed to the tailings ponds by a factor of 10. A full-scale, HDS lime neutralization treatment plant for an average flow rate of 1500 m3/hr was designed and was commissioned in early 1998 in collaboration with Colder Associates, Ottawa, Canada. So far, the full-scale treatment plant has been generating a sludge with more than 30% solids content, exceeding its target value of 12% solids. It produces excellent effluent quality, and scaling in the handling equipment is virtually eliminated. The sludge has dense, easily settable granular particles rather than fluffy flocs, yet has low viscosity that facilitates its unassisted gravity flow. The process has resulted in an increase in the treated water volume. The rate of lime consumption per unit volume of water treated also decreased. The process principles and the steps taken in process development will be discussed and the results obtained to date will be summarized in this communication.

Abstract: A considerable part of water obtained by drainage of Polish coal-mines is saline which creates substantial ecological problems. The load of salt (mainly sodium chloride) amounts to 5 min t/year. Despite the utilisation of saline coalmine waters is considered to be the most adequate method of solving ecological problems caused by this kind of water in Poland there are only two installations utilising coal-mine waters and producing 100,000 t salt per year. In the case of the most concentrated waters, the so-called coal-mine brines, the method of concentrating by evaporation in twelve-stage expansion installation or vapour compression is applied, after which sodium chloride is manufactured. In the case of low salinity waters they are preconcentrated first by RO method. High energy consumption in above-mentioned methods of evaporation is a considerable restriction in the utilisation of coal-mine brines. An obstacle in the application of low energy evaporation processes, e.g. multi-stage flash, is the high concentration of calcium and sulphate ions in the coal-mine waters.