Evaluation of Phosphate Materials for Control of Acid Production in Pyritic Mine Overburden

Abstract

Acid mine drainage is a serious and pervasive threat to surface and groundwater quality in the USA. Recent research has indicated that phosphate can be effective at immobilizing Fe and inhibiting the production of acid associated with the oxidation of pyritic mine wastes. Four phosphate materials were replicate tested for their ability to inhibit acid production from pyritic coal overburden using a soxhlet humidity cell leaching technique. These materials included two apatite ores (Comineo ore and Texas Gulf ore) at an application rate of 30 g kg−1 by weight apatite [Ca5(PO4)3OH] and two byproducts of the phosphate industry (Cominco waste and Stauffer sludge) at rates of 10, 30, and 50 g kg−1 apatite by weight. Results of leachate analyses indicate that all phosphate sources at all rates of application resulted in significant (P ≤ 0.05) decreases in titratable acidity vs. a control Acidity reductions ranged from a low of 7% for samples treated with Cominco waste (10 g kg−1) to a high of 67% for Texas Gulf ore‐treated samples. Texas Gulf ore, Stauffer sludge (10, 30, and 50 g kg−1) and Cominco waste (10, 30, and 50 g kg−1) significantly reduced dissolved total Fe concentrations in leachate, with Stauffer sludge (50 g kg−1) and Texas Gulf ore producing the most notable diminutions (62 and 63%, respectively). Maximum decreases in sulfate (SO2−4) concentrations of 26, 20, and 25% were achieved by applications of Texas Gulf ore and Stauffer sludge (30 and 50 g kg−1), respectively. The more effective overall performance of the Stauffer sludge and Texas Gulf ore was attributed to the considerably greater relative surface area and P solubility of these amendments. Results of a scanning electron microscope examination of amendments corroborate these findings.

Acid Rock Drainage or Not—Oxidative vs. Reductive Biofilms—A Microbial Question

“…The additions reduced the acidity generated, but the lowest dosage of NPR produced better results than higher dosages. The approach was abandoned by industry [6][7][8][9][10][11][12][13][14][15][16][17] for various reasons. The results, though, were intriguing to ecologists, possibly indicating microbial involvement.…”

“…The literature of the mid-1980s is reviewed as it pertains to the formation of iron phosphate coatings on the mineral surface. This avenue was intensely pursued with various phosphate containing materials to limit sulphide oxidation [6][7][8][9][10][11][12][13][14][15][16][17]. Among these research efforts, one using NPR ore from a phosphate mine in North Carolina caught our attention.…”

The Use of Basic Oxygen Steel Furnace Slag (Bos) as a High Surface Area Media for the Removal of Iron From Circum Neutral Mine Water

“…Environmental pressures to improve the chemical and biological quality of fresh surface waters have led to an increased need to remediate these sources of pollution. Sustainable treatment options have been the focus of extensive research in both the US and the UK (Spotts and Dollhopf 1992, Hedin et al 1994, Gazea et al 1996, Younger 2003a. Treatment of mine waters be they net-acidic or net-alkaline, can take two broad forms: active or passive.…”

Toward Source Control of Acid Rock Drainage

“…Phosphate has a number of attributes that make it attractive for source control of ARD (Renton and Stiller, 1989;Spotts and Dollhopf, 1992;Kalin et al, 1998;Conca and Wright, 2001;Harris and Lottermoser, 2003). In addition to its potential for armoring sulfide minerals, phosphate precipitates Fe 3+ at relatively low pH thereby removing this oxidant from solution.…”