Experimental study on prevention of acid mine drainage by silica coating of pyrite waste rocks with amorphous silica solution

Abstract

Acid mine drainage (AMD) is a widespread environmental problem associated with working and abandoned mining operations. It results from the microbial oxidation of pyrite in the presence of water and air, affording an acidic solution that contains toxic metal ions. Pyrite microencapsulation, utilizing silica coating, is a novel approach for controlling AMD that has been shown to be very effective in controlling pyrite oxidation. The roles of the solution pH and silica concentration in the formation mechanism for the AMD-preventing coating were investigated. A silica coating can be formed from silica solution at pH 7, at which the amount of Fe eluted from pyrite into the solution is small. No coating was formed at other pH values, and the amounts of eluted Fe were larger than at pH 7, especially at pH 11. The silica coating forms from 2,500 to 5,000 mg/L silica solutions, but not from 0 or 1,000 mg/L silica solutions. The coating formation rate was slower in the 2,500 mg/L silica solution than in the 5,000 mg/L silica solution. The formation of silica coating on pyrite surfaces depends on three main steps: formation of Fe(OH) 3 on the surface of pyrite, reaction between Fe(OH) 3 and silicate in the solution on the pyrite surface, and growth of the silica layer on the first layer of silica. The best pH condition to enable these steps was around 7, and the silica coating formation rate can be controlled by the concentration of silica.

Silicate Covering Layer on Pyrite Surface in the Presence of Silicon–Catechol Complex for Acid Mine Drainage Prevention

“…Figure 2 shows that pyrite sample treated for 6 h has the lowest oxidation rate and largest suppression effect. This result is consistent with the study conducted by Bessho et al 12) that showed equilibrium pHs of silica solutions were reached after 6 h of stirring. Pyrite sample treated for 1 h shows the lowest suppression effect.…”

Heavy load and high potential: anthropogenic pressures and their impacts on the water quality along a lowland river (Western Bug, Ukraine)

“…The mining region was characterised by large inputs of dry matter that may be caused by surface runoff from uncovered soil and even erosion. Negative impacts of acid mine drainage on river ecosystems have been reported in many cases (Bessho et al 2010;Xiao et al 2010), but, in contrast to our expectations, an impact of acid mining drainage on the Western Bug River was not detected within the surface water of this region. Interestingly, the Rata River contributed the least amount of pollution among the tributaries and physical, chemical indicators suggested an overall moderate ecological state comparable to the headwater region at Buzhok and the Zolochivka River (Fig.…”

Experimental Study on the Optimum Preparation of Bentonite–Steel Slag Composite Particles

“…Total alkalinity (mg/L) = C × (P + M) × 50.05 V × 1000 (2) where C is the concentration of the HCl standard solution (mol/L); P is the HCl consumption after the addition of the phenolphthalein reagent (mL); M is the HCl consumption after the addition of the methyl orange reagent (mL); V is the volume of the water sample (mL), and 50.05 is the molar mass of calcium carbonate (1/2CaCO 3 ) (g/mol). The loss rate of the composite particles was calculated as follows:…”

“…Acid mine drainage (AMD) is a major pollution source in mining areas [1,2]. AMD has a pH < 3, and contains high concentrations of toxic elements, such as heavy metal ions, which cannot be reused [3,4].…”