Abstract: Under environmental conditions, arsenic (As) reveals anionic behavior and is converted into various forms in accordance with the Eh/pH condition. This causes the difficulty of treating As with other heavy metals in tailing. This study was carried out to develop the immobilization method of arsenic in tailing as ferric arsenate (FeAsO4) using hydrogen peroxide. According to experimental results, the extracted concentrations of arsenic and iron (Fe) from tailing were reduced up to 84% and 93%, respectively. In the experiment using pure Pyrite (FeS2) and As solution, As concentration decreased with an increase of hydrogen peroxide dosage. The experimental results of re-extraction showed that only 10% of As and 20% of Fe were extracted in the case of using hydrogen peroxide. As a result, the long-term stability of this method was clarified.

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: Contact of oxygen contained in air and water with mining materials can increase the solubility of metals. In heaps leached by cyanide, metals can also be made soluble through complexation with cyanide. During closure, water in heaps, and water collected in mine workings and pit lakes may require treatment to remove these metals. In situ microbiological treatment to create reductive conditions and to precipitate metals as sulfides or elemental metal has been applied at several sites with good success. Treatment by adding organic carbon to stimulate in situ microbial reduction has been successful in removing arsenic, cadmium, chromium, copper, iron, lead, manganese, mercury, nickel, selenium, silver, tin, uranium, and zinc to a solid phase. Closure practices can affect the success of in situ treatment at mining sites, and affect the stability of treated materials. This paper defines factors that determine the cost and permanence of in situ treatment.