| Popis: |
Remediation of acid mine drainage (AMD) is an expensive process. Iron sediment from AMD treatment can be industrially significant and sold as pigment which can mitigate the remediation cost. An AMD treatment plant in Millfield, Ohio is being constructed for this purpose with the goal of selling commercial grade iron pigment while restoring an impaired stream. The ferrous iron in the AMD is oxidized, and then the hydrolyzed ferric iron is settled. However, to produce high-quality pigment, the pH must be kept at 4.5 or lower, posing a challenge for adequate settling. In this research, ten different commercial polymers were evaluated to increase the settling rates of the iron particles at low pH. The jar test was implemented to select the best polymer and optimize the dose to reduce the turbidity of the sample. The polymers NS-6650 and 6050 from Neo-Solutions, Inc. (Beaver, PA) removed more than 99% turbidity at 0.2 mg/L dosage, making them the best flocculants tested. In terms of calculated flocculent contamination, this flocculant dose yielded 99.95% pigment purity. The flocculants and dose were further tested for sedimentation, which resulted in iron settling rate of 0.15-0.25 ft/min. A clarifier design rise rate of 0.5-0.9 gpm/ft2 (700-1250 gpd/ft2) and diameter of 35-50 ft was recommended for the approximate Truetown seep flowrate of 2 cfs expecting 3-3.5% clarifier underflow solids content. For dewatering this sludge produced at low pH, vacuum filtration and filter press were evaluated in this research. The vacuum filtration did not appear as a suitable option because of longer cake formation time and high suspended solids content in the filtrate. However, the filter press showed feasible performance producing filter cakes with 20-25% solids content and indicating further improvement up to 30% cake solids with water effluent TSS |
