EFFECT OF PREPARATION METHOD ON ADSORPTION CAPACITY OF ACID MINE DRAINAGE SLUDGE FOR PHOSPHORUS

The anthropogenically induced eutrophication of the Chesapeake Bay is a pressing environmental issue, and the development of cost-effective, sustainable methods of nutrient removal is essential to its remediation. The use of acid mine drainage (AMD) sludge, a byproduct of coal mine water neutralization treatment, as an adsorbent has been proposed as an alternative method for phosphorus (P) sequestration. Drying methods – oven-dry, freeze-thaw, and freeze-dry – were investigated for their effects on the adsorption capacity of AMD sludges from three different locations in Pennsylvania. Batch adsorption tests were conducted using six initial concentrations of total dissolved phosphate – 1, 2, 5, 10, 20, and 50 mg/L as P – and a contact time of 24 hours. Treated sludges were characterized by SEM imagery and BET specific surface area analysis.

For all of the sludges tested, P adsorption was promising, with removal efficiencies measured in excess of 99%. Freundlich isotherms were fit to experimental data and Freundlich coefficients were used as a measure of adsorption capability. Overall, drying method was found to have no statistical significance (p=0.38), but there were differences between sludge sources (p<0.001) and differences in treatment effect amongst AMD sludge sources (p=0.001). For two of the three sludge sources tested, freeze-thawed and freeze-dried sludges had higher adsorption capacities than oven-dried sludges. SEM images showed oven-dried sludges to be welded and crystalline with minimal internal porosity, whereas freeze-thawed and freeze-dried sludges appeared to be fine-grained aggregates. BET specific surface areas, measured over the range of 87-243 m²/g, did not show a consistent pattern based on drying method, but differed among sludge sources.

In summary, our findings indicate that the method of sludge drying has less impact on sorption performance than the source of the sludge. Overall, however, all of the sludge sources, under all of the conditions tested, were effective at removing P from the water, suggesting that AMD sludges should therefore be considered a useful resource for water remediation, rather than a burdensome waste.