Stabilization of lead bearing sludge by utilization in fly ash-slag based geopolymer

Abstract

The present work demonstrates the utilization of three important industrial by-products; fly ash (FA), ground blast-furnace slag (GBFS), and lead-bearing sludge (LS) in preparing geopolymer as a replacement for cement binder. The feasibility of preparing high-performance geopolymers by mixing various ratios of industrial by-product fractions (FA, GBFS and LS) with alkali activator is examined, the prepared geopolymers were cured at room temperature up to 90 days. Various parameters such as setting time, mechanical strength, hydration characteristics and leaching behaviour of lead were evaluated The results show that at percentages of 70–80 mass% GBFS and 20–30 mass% FA, a reasonable compression strength compared to the past of ordinary Portland cement (OPC) is obtained. However, the substitution of 40 mass% GBFS or more with FA causes significant reductions in compressive strength at all curing times.By the substitution of 20 mass% GBFS with LS compared to the optimum percentage of 80 mass% GBFS and 20 mass% FA, the studied mechanical properties of the produced mixture (60 mass% GBFS, 20 mass% FA, and 20 mass% LS) were enhanced. The Pb-concentration (mg/l) in the leachate of this mixture was below the safe limit of toxicity characteristic leaching procedure (TCLP). The partial or total substitution of Portland cement by these materials provides an ideal way to get rid of waste in a good and environmentally safe manner.