Potential of mining, agro-industrial, and urban wastes for the remediation of acidic mine water

<p>Mining is a crucial industry worldwide because of its economic and social importance. However, the increasing number of operating mines raises major concerns for health and the environment. The intense mining activity generates large quantities of wastes associated with several environmental problems. For example, the generation of acid mine drainages (AMD) by oxidation of sulphide ores stored in tailings deposits, leachates high concentrations of potentially harmful elements (PHEs), which poses severe pollution problems to the environment (aquatic and terrestrial ecosystems). This study evaluates the acid neutralisation capacity and the removal effectiveness of inorganic PHEs present in an AMD of different waste materials. This study is a first approach to future studies to develop pilot remediation studies using designed waste-derived Technosols. The waste used includes 4 mining wastes (iron oxide and hydroxide sludges [IO], marble cutting and polishing sludge [MS], gypsum spoil [GS], and carbonated waste from a peat extraction [CW]), 3 urban wastes (composted sewage sludge [WS], bio-stabilised material from municipal solid waste [BM], and vermicompost from pruning and gardening [VC]), and 3 agro-industrial wastes (2 solid olive-mill by-products [OW, OL] and composted greenhouse waste [GW]). All waste materials were spiked with the acidic water (AMD<sub>L</sub>) prepared in the laboratory from the oxidation of pyritic tailings from the Aznalcóllar mine accident (1998). Afterward, they were stirred for 24 h and filtered, separating the waste (solid phase) from the leachate (liquid phase). In the leachate (AMD<sub>L</sub> treated), pH<sub>(L) 1:5</sub>, EC<sub>(L) 1:5</sub>, and inorganic PHEs concentrations were measured, the latter by ICP-MS. The acidic water showed a strongly acidic character (pH<sub>(L)</sub> ~ 2.89), high salinity (EC<sub>(L)</sub> ~ 3.76 dS m<sup>-1</sup>), and high concentrations of PHEs. Among them, As, Cd, Cr, Cu, Ni, Pb, Sb, Th, Tl, U, V, Y, and Zn stood out since they far exceed various legal limits widely used worldwide and/or because their high toxicity to humans, animals, plants or microorganisms. The most abundant were Zn (32.21 mg l<sup>-1</sup>), Cu (6.24 mg l<sup>-1</sup>), As (2.86 mg l<sup>-1</sup>), Sb (0.82 mg l<sup>-1</sup>), Pb (0.60 mg l<sup>-1</sup>), and Cd (0.45 mg l<sup>-1</sup>). All wastes were effective in neutralising the acidic pH<sub>(L)</sub> of the AMD, as the leachates showed pH<sub>(L)</sub> close to 7. In contrast, changes in the EC<sub>(L)</sub> have been very irregular among the wastes used. In general, all wastes have been effective in adsorbing the PHEs. Inorganic wastes have been much more effective than organic ones, with adsorption efficiencies above 95% for many of the PHEs (particularly for those in higher concentrations). The waste with the best remediation behaviour were IO, CW, MS, GS, and VC. Conversely, GW and WS were the worst at removing PHEs present in AMD. Therefore, this study shows that many of wastes tested are suitable for the construction of Technosols from these wastes to prevent soil pollution by AMD discharge.</p>

Photoelectrochemical Concurrent Hydrogen Generation and Heavy Metal Recovery from Polluted Acidic Mine Water

The feasibility of a solar-driven photoelectrochemical process to generate hydrogen fuel from metal mine polluted water while simultaneously recovering heavy metals has been explored. Electron transport from the photoanode to...

Effectiveness of Fly Ash and Red Mud as Strategies for Sustainable Acid Mine Drainage Management

Acid mine drainage (AMD), red mud (RM) and coal fly ash (CFA) are potential high environmental pollution problems due to their acidity, toxic metals and sulphate contents. Treatment of acidic mine water requires the generation of enough alkalinity to neutralize the excess acidity. Therefore, red mud types from Germany and Greece were chosen for the neutralization of AMD from South Africa, where this problem is notorious. Because of the high alkalinity, German red mud is the most promising precipitation agent achieving the highest pH-values. CFA is less efficient for a neutralization and precipitation process. An increase in temperature increases the adsorption kinetics. The maximum pH-value of 6.0 can be reached by the addition of 100 g German red mud at 20 °C to AMD-water with an initial pH value of 1.9. German red mud removes 99% of the aluminium as aluminium hydroxide at pH 5.0. The rare earth elements (yttrium and cerium) are adsorbed by Greek red mud with an efficiency of 50% and 80% at 60 °C in 5 min, respectively.

Comprehensive review on wastewater discharged from the coal-related industries – characteristics and treatment strategies

Wastewaters discharged from various coal-related activities deteriorate fresh water quality and inflict possibilities of groundwater contamination. Their characteristics mostly depend on the parent coal properties, though some of the pollutants are cyanide, thiocyanate, ammonia, phenol, heavy metals and suspended solids. This paper has reviewed the treatment techniques along with the characteristics of all such kinds of wastewater and also identified the challenges and future perspectives. Primarily, demineralization of coal can attenuate and control release of pollutants in wastewaters if implemented successfully. Mine water from non-lignite mines can be purified using simple techniques, for its reutilization. Acidic mine water and leachates can be treated using passive bioreactors with microbial activity, different organic substrates and limestone drains. Additionally bio-electrochemical systems, membranes, macrocapsules, zeolite filters, ores, physical barriers, and aquatic plants can also be used at various stages. Coal washery wastewater can be treated using natural coagulants obtained from plant extracts along with conventional coagulants. Nitrification and denitrification bacteria fixed in reactors along with activated carbon and zero-valent iron can treat coke oven wastewater. Some other sophisticated techniques are vacuum distillation, super critical oxidation, nanofiltration and reverse osmosis. Practical use of these methods, wisely in an integrated way, can reduce freshwater consumption.