Stabilization of Heavy Metals in Portland Cement Matrix: Effects on Paste Properties

Effects of heavy metals on the physical and chemical properties of cement pastes were studied using different types of cement, four metal oxides and four soluble metal salts. Type I (high aluminate content) and Type V (low aluminate content) cements were used to study the effects of their chemical differences on paste properties and metal stabilization. Fresh pastes were tested for workability, initial setting times, and heats of hydration. Hardened pastes were tested for strength and leachability by both TCLP and column leaching with acetic acid. Initial setting times for pastes were significantly retarded by cadmium oxide and either form of lead and flow also decreased. Effects on setting time, slump area, and increased conduction calorimetry induction times are more pronounced with higher levels of lead and cadmium oxide. Addition of soluble chromium(III) chloride caused accelerated setting, higher paste temperatures, and smaller slump areas with both types of cement. In general Type V cement pastes with either soluble salts or oxides exhibit longer setting and induction times, and larger slump areas compared to Type I pastes. Slow setting pastes had low three day strengths while fast setting pastes had high strengths at this age. However, the ninety day strengths of cement pastes is near control strengths for both Type I and Type V cements. Leaching results were similar to those found by other workers. In these very cement-rich solids, chromium and cadmium were well stabilized but higher lead and mercury leaching was observed.