Recovery of marketable iron oxide from mine drainage in the USA

Abstract

Iron oxide sludge was recovered from a channel at an abandoned coal mine, processed, and used as a raw material in pigment production. The site is a former coal mining and processing facility in southwestern Pennsylvania. Over the last 60 years, a channel carrying the mine discharge (9500 m3/day, pH 6.2, Fe 72 mg/L, alkalinity 312 mg/L as CaCO3) had filled with iron sludge. As a ‘proof-of-principle’ project, approximately 2000 tons of sludge were removed and processed. The sludge was screened and dewatered using frame filter presses. Screening removed vegetative debris, litter, and coal refuse. Dewatering increased the solids content of the product from 25–30% (in place sludge) to 50–52%. A total of 1000 tons of product were trucked to a pigment manufacturer, where it was further dried, calcined, and milled. The company is using the finished product to produce a burnt sienna pigment that is used in a variety of colouring applications. The mine drainage product is replacing natural (mined) sources of iron oxide obtained in the United States and imported from Mediterranean and Asian countries. Work is continuing on developing methods that will decrease the processing costs, so that iron oxide can be produced from mine drainage in a profitable manner.