Remediation of electric arc furnace dust leachate by the use of cementitious materials: A column-leaching test

Abstract

Disposal of industrial solid wastes in a hydrologic environment can cause environmental risks due to the mobility of toxic trace elements. It is increasingly important to find simple and inexpensive treatments to remove undesirable elements from industrial solid wastes. One of the most important problems in the secondary steel mill industry is the disposition of dusts produced from electric arc furnace. A large quantity (10--20 kg) of electric arc furnace dust (EAFD) is generated per ton of steel produced. The Toxicity Characteristic Leaching Procedure (TCLP) shows that the total Cr and Cr (VI) concentrations (9.7 and 6.1 mg/L respectively) from the EAFD studied exceeded the Toxicity Characteristic Regulatory Level. Some heavy metals of EAFD like chromium are toxics and have high solubility. Chromium (VI) is particularly problematic because it must initially be reduced before fixed in an insoluble phase. To counter this problem, the use of ordinary Portland cement (OPC) and ground granulated blast furnace slag (GGBFS) was investigated. Column leaching test was performed to evaluate the leaching of EAFD amended with GGBFS and OPC under dynamic conditions simulating heap leaching. The goal of this study is to fred a simple and economic way to decrease contaminants in the leachate. Test columns have been set up to evaluate the effect of alkaline additives (OPC and GGBFS) on the geochemistry of drainage water. The control column consists of EADF only. A set of columns presents the effect of the addition of 5% by mass of OPC or GGBFS mixed homogeneously with the EAFD. Another set of columns was set up with the same quantities of OPC and GGBFS but concentrated at the base of the EAFD simulating a liner. Columns were fed three times weakly during 1 month. The parameters monitored after each flush of water include leachate volume, pH, electrical conductance and water quality (Cr-Ni-Pb-Zn concentrations). The leaching of the control (EAFD only) presents high Cr concentration. The addition of GGBFS and OPC increases the pH conditions and decreases metal concentrations. The concentration of OPC and GGBFS at the base of the EADF as a liner was the more efficient disposition. The use of a mixture of EAFD with 5% of OPC or GGBFS applied at the base of EADF heap is a simple and economic way to remove contaminant. In spite of a significant decrease in Cr concentration, values remain slightly above regulatory level.