No abstract

No abstract

The formation of acid mine drainage (AMD), a highly acidic and metal-rich solution, is the biggest environmental concern associated with coal and mineral mining. Once produced, AMD can severely impact the surrounding ecosystem due to its acidity, metal toxicity, sedimentation and other deleterious properties. Hence, implementations of effective post-mining management practices are necessary to control AMD pollution. Due to the existence of a number of federal and state regulations, it is necessary for private and government agencies to come up with various AMD treatment and/or control technologies. This review describes some of the widely used AMD remediation technologies in terms of their general working principles, advantages and shortcomings. AMD treatment technologies can be divided into two major categories, namely prevention and remediation. Prevention techniques mainly focus on inhibiting AMD formation reactions by controlling the source. Remediation techniques focus on the treatment of already produced AMD before their discharge into water bodies. Remediation technologies can be further divided into two broad categories: active and passive. Due to high cost and intensive labor requirements for maintenance of active treatment technologies, passive treatments are widely used all over the world. Besides the conventional passive treatment technologies such as constructed wetlands, anaerobic sulfate-reducing bioreactors, anoxic limestone drains, open limestone channels, limestone leach beds and slag leach beds, this paper also describes emerging passive treatment technologies such as phytoremediation. More intensive research is needed to develop an efficient and cost-effective AMD treatment technology, which can sustain persistent and long-term AMD load.

No abstract

The influence of pH, ionic strength, ligands (Cl, SO4, PO4), and metals (Ni and Pb) on the adsorption of Hg(II) by quartz and gibbsite was investigated to better understand the Hg(II) adsorption process and the impact of metals and ligands on this process. The triple layer model (TLM) was used to simulate Hg(II) adsorption on both surfaces. Mercury(II) adsorption from a 0.6 μM Hg(II) solution varies as a function of pH, increasing to an adsorption maximum with increasing pH before tailing off to a constant level at high pH values. The pH at which maximum Hg(II) adsorption occurs (pHmax ≈ 4.5) is comparable to the pKa (3.2) for the hydrolysis of Hg2+ to form Hg(OH)02 Further, the Hg(II) adsorption edge shifts to much higher pH values in the presence of 0.001 M and 0.01 M Cl, which also corresponds to the pH at which Hg(OH)02 is predicted to form. Only minor deviations in the degree of adsorption and the shape of the Hg(II) adsorption edge are influenced by ionic strength, suggesting the formation of inner‐sphere surface complexes. However, Hg(II) adsorption can only be successfully modeled with consideration of the formation of both an outer‐sphere surface complex [≡XO−–HgOH+] and an inner‐sphere surface complex [≡XOHg(OH)−2]. Swamping concentrations (0.01 M) of SO4 and PO4 reduced Hg(II) adsorption on quartz, a result of the predicted formation of Hg(OH)2SO2−4, Hg(OH)2H2PO−4, and Hg(OH)2–HPO2−4 aqueous species (the adsorption edge and pHmax were not influenced). The presence of SO4 also decreased Hg(II) retention by gibbsite, which was also attributed to the formation of the Hg(OH)2SO2−4 ion pair; however, the presence of PO4 increased Hg(II) retention by gibbsite, which was attributed to the formation of a phosphate bridge [≡AlOPO3Hg(OH)2−2]. Mercury(II) adsorption was decreased in the presence of 14 μM Pb and 48 μM Ni, and most noticeably in the quartz system. The adsorption of Hg(II), when in competition with Pb or Ni, could not be simulated by the TLM without the reoptimization of the Hg(II) outer‐ and inner‐sphere log Kint values. Intrinsic Hg(II) adsorption constants derived from single‐element systems could not be employed to simulate adsorption in multi‐element, competitive systems.

Efficient utilization of biosolids P for agronomic purposes requires accounting for differences in the phytoavailability of P in various biosolids. Greenhouse studies were conducted with a common pasture grass grown in two P-deficient soils amended with 12 biosolids and a commercial fertilizer (triple superphosphate, TSP) to quantify P uptake and to assess the relative phytoavailabilities of the P sources. Biosolids were grouped into three general categories of phytoavailability relative to TSP: high (> 75% of TSP), moderate (25-75% of TSP), and low (< 25% of TSP). Two biosolids, produced via biological phosphorus removal (BPR) processes, were in the high category, and mimicked fertilizer P with regard to P phytoavailability. Most biosolids produced by conventional wastewater and solids digestion and additional treatments like composting were in the moderate category. Also included in this category was a BPR that had been pelletized and another BPR supplemented with Al. The low category included biosolids containing greater than normal (> 50 g kg(-1)) total Fe and Al concentrations and processed to high (> 60%) solids content.

No abstract

various biosolids to assure efficient agronomic utilization of biosolids P. Efficient utilization of biosolids P for agronomic purposes requiresWhen P considerations dictate biosolids application, accounting for differences in the phytoavailability of P in various biosolids. Greenhouse studies were conducted with a common pasture the 1995 USEPA design manual (USEPA, 1995) advises grass grown in two P-deficient soils amended with 12 biosolids and consideration of the "relative effectiveness" (50%) of a commercial fertilizer (triple superphosphate, TSP) to quantify P biosolids P compared with fertilizer P. No literature is uptake and to assess the relative phytoavailabilities of the P sources.cited to support the 50% value, but several researchers Biosolids were grouped into three general categories of phytoavaila-(e.g., de Haan, 1980; Hall and Williams, 1984; Coker bility relative to TSP: high (Ͼ75% of TSP), moderate (25-75% of and Carlton-Smith, 1986) report ranges from 10 to 100% TSP), and low (Ͻ25% of TSP). Two biosolids, produced via biological effectiveness relative to fertilizer P determined in greenphosphorus removal (BPR) processes, were in the high category, and house studies. Canadian regulators (Ontario Ministry mimicked fertilizer P with regard to P phytoavailability. Most biosolids of Environment and Energy and Ontario Ministry of produced by conventional wastewater and solids digestion and addi-