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Mitchell, P., & Wheaton, A. (1999). From environmental burden to natural resource; new reagents for cost-effective treatment of, and metal recovery from, acid rock drainage. In D. E. Goldsack, N. Belzile, P. Yearwood, & G. J. Hall (Eds.), Sudbury '99; Mining and the environment II; Conference proceedings.
Abstract: Acid rock drainage remains the greatest environmental issue faced by the mining sector and as the new millennium approaches, low capital/operating cost treatments remain elusive. Therefore as part of an ongoing process to develop a leading edge, innovative and cost-effective approach, pilot trials were conducted by KEECO in collaboration with the New Bunker Hill Mining Company on a substantial and problematic metal-contaminated acid flow, emanating from underground workings at the Bunker Hill Mine, Idaho. The aims of the work were fourfold. First to assess the capacity of KEECO's unique Silica Micro Encapsulation (SME) reagents and associated dosing systems to cost-effectively decontaminate the acid flow to stringent standards set by the U.S. Environmental Protection Agency (USEPA), where alternative and standard technologies had failed. Second, to demonstrate that treatment using a compact system suitable for underground installation. Third, to demonstrate that the treatment sludge had enhanced chemical stability in absolute terms and relative to standard approaches. Fourth, to examine the potential for resource recovery via sequential precipitation. Although the focus to date has been the development of a cost-effective treatment technology, the latter aim was considered essential in light of the growing pressure on all industrial sectors to develop tools for environmentally sustainable economic growth and the growing demands of stakeholders for improved resource usage and recycling. Two phases of work were undertaken: a laboratory-based scoping exercise followed by installation within the mine workings of a compact reagent delivery/shear mixing unit capable of treating the full flow of 31 L s (super -1) . At a dose rate of 2.0 g L (super -1) (equivalent to a final treated water pH range of 7-9), the SME reagent KB-1 reduced metal concentrations to levels approaching the U.S. Drinking Water Standards, which no other treatment piloted at the site had achieved. Based on the USEPA's Toxicity Characteristic Leaching Procedure, the sludge arising from the treatment was classified as non-hazardous. Operating costs compared favourably with those of lime use, while estimated capital costs were considerably lower due to the compact nature of the reagent delivery system and the rapid settling characteristics of the treatment sediment. Resource recovery was attempted using a two-stage selective precipitation approach. The first stage involved pH adjustment to 5.5 (by addition of 1.5 g L (super -1) of KB-1) to produce a sludge enriched in aluminium, iron and manganese, with lesser amounts of arsenic, nickel, lead and zinc. Further KB-1 addition to a total of 2.1 g L (super -1) generated sludge enriched in zinc (33% by dry weight), demonstrating that resource recovery is theoretically feasible. Further work on downstream processing is required, although it is considered that the most likely route for zinc metal recovery will be high temperature/pressure due to the chemically inert nature of the zinc-rich sediment.
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Nakazawa, H. (2006). Treatment of acid mine drainage containing iron ions and arsenic for utilization of the sludge. Sohn International Symposium Advanced Processing of Metals and Materials, Vol 9, , 373–381.
Abstract: An acid mine drainage in abandoned Horobetsu mine in Hokkaido, Japan, contains arsenic and iron ions; total arsenic ca.10ppm, As(III) ca. 8.5ppm, total iron 379ppm, ferrous iron 266ppm, pH1.8. Arsenic occurs mostly as arsenite (As (III)) or arsenate (As (V)) in natural water. As(III) is more difficult to be remove than As(V), and it is necessary to oxidize As(III) to As(V) for effective removal. 5mL of the mine drainage or its filtrate through the membrane filter (pore size 0.45 mu m) were added to arsenite solutions (pH1.8) with the concentration of 5ppm. After the incubation of 30 days, As(III) was oxidized completely with the addition of the mine drainage while the oxidation did not occur with the addition of filtrate, indicating the microbial oxidation of As(III). In this paper, we have investigated the microbial oxidation of As(III) in acid water below pH2.0.
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Dempsey, B. A., & Jeon, B. - H. (2001). Characteristics of sludge produced from passive treatment of mine drainage. Geochem.-Explor. Environ. Anal., 1(1), 89–94.
Abstract: In the 1994 paper by Brown, Skousen & Renton it was argued that settleability and wet-packing density were the most important physical characteristics of sludge from treatment of mine drainage. These characteristics plus zeta-potential, intrinsic viscosity, specific resistance to filtration, and coefficient of compressibility were determined for several sludge samples from passive treatment sites and for several sludge samples that were prepared in the laboratory. Sludge from passive systems had high packing density, low intrinsic viscosity, low specific resistance to filtration and low coefficient of compressibility compared to sludge that was produced after addition of NaOH.
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Heal, K. V., & Salt, C. A. (1999). Treatment of acidic metal-rich drainage from reclaimed ironstone mine spoil. Water Sci. Technol., 39(12), 141–148.
Abstract: Ironstone mine spoil leaves a legacy of land contamination and diffuse water pollution with acidic, metal-rich drainage. Reclamation for woodland may exacerbate water pollution due to spoil amendment and disturbance. Constructed wetland systems (CWS) are increasingly used for treating acid mine drainage but their performance is poorly understood. A combined approach was used to reclaim the Benhar ironstone spoil heap in Central Scotland. Trees have been planted in spoil treated with dried pelleted sewage sludge, limestone and peat. Spoil drainage (pH 2.7, 247 mg l-1 total Fe) passes through a CWS. Spoil throughflow, surface water chemistry and CWS performance were monitored for 12 months after reclamation. Acidity, Fe, Mn and Al concentrations declined in throughflow after reclamation, although this effect was not uniform. Soluble reactive P has been mobilised from the sewage sludge in residual areas of spoil acidity, but losses of other nutrients were short-lived. The CWS removes on average 33 % and 20-40 % of acidity and metal inputs but removal rates decrease in winter. Spoil reclamation has been successful in enabling vegetation establishment but has also increased Fe and Mn concentrations in surface drainage from the site, even after passage through the CWS.
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Aube, B. C., & Zinck, J. M. (1999). Comparison of AMD treatment processes and their impact on sludge characteristics.
Abstract: Lime neutralisation for the treatment of acid mine drainage is one of the oldest water pollution control techniques practised by the mineral industry. Several advances have been made in the process in the last thirty years, particularly with respect to discharge concentrations and sludge density. However, the impact of different treatment processes on metal leachability and sludge handling properties has not been investigated. A study of treatment sludges sampled from various water treatment plants has shown that substantial differences can be related to the treatment process and raw water composition. This study suggests that sludge densities, excess alkalinity, long-term compaction properties, metal leachability, crystallinity and cost efficiency can be affected by the neutralisation process and specific process parameters. The study also showed that the sludge density and dewatering ability is not positively correlated with particle size as previously suggested in numerous studies. The treatment process comparisons include sludge samples from basic lime treatment, the conventional High Density Sludge (HDS) Process, and the Geco HDS Process.
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