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: Treatment of radioactively-contaminated and metal-laden mine waters and of seepage fiom tailings ponds and waste rock piles is among the key issues facing WISMUT GmbH in their task to remediate the legacy of uranium mining and processing in the Free States of saxony and rhuringia, Federal Republic of Germany. Generally, contaminant loads of feed waters wn aimnisn over time. At a certain level of costs for the removal of one contaminant unit, continued operation of conventional water treatment plants can hardly be justified any longer. As treatment is still required for water protection, there is an urgent need for-the development and implementation of more cost efficient technologies. WISMUT GmbH and BioPlanta GmbH have studied the suitability of helophye species for contaminant removal from mine waters. In a fust step, original waters were used for an in vitro bioassay. The test results allowed for the determination of the effects of biotic and abiotic factors on helophy'tes'tolerancer ange, growth, and uptake capability of radionuclides and metals. Test series were carried out using Phiagmites australis, Carex disticha, Typha latifolia, and Juncus effusus. Relevant cont-aminant components of the mine waters under investigation included uraniunl iron, arsenic, manganese, nickel, and copper. Investigations led to a number of recommendations conceming plant selection for specific water treatment needs. In a second step, based on these results, a constructed wetland was built in l99g as a pilot plant for the treatment of flood waters liom the pöhla-Tellerhäuser mine and went on-line. Relevant constituents of the neutral flood waters include radium, iron, and arsenic. This wetland specifically uses both physico-chemical and microbiological processes as well as contaminant accumulation by helophytes to achieve the treatment objectives. with the pilot plant in operation for three years now, average removal rates achieved are 95 Yo for kon, 86 yo for arsenic, and 75 % for raäium. WISMUT GmbH intends to put a number of other projects of passive/biological mine water treatment into operation before the end of 2001_