Immobilization of Cr(VI) in bagasse ash blended cement pastes

The aim of the present work is to study the hydration characteristics and immobilization of Cr(VI) in bagasse ash blended cement pastes by setting time, compressive strength, bulk density, total porosity and immobilization efficiency measurements as well as XRD, FTIR and SEM techniques. It was investigated that hydration characteristics of bagasse ash blended cement pastes were enhanced especially at later ages of hydration. Immobilization of Cr(VI) in bagasse ash blended cement pastes reduces their setting time, accelerates hydration reactions due to precipitation of CaCrO4 and affects the pore formation mechanism of hydrated cement pastes. The alkalinity of bagasse ash blended cement pastes were reduced due to pozzolanic action. Hence, the rate of precipitation of CaCrO4 decreases with bagasse ash content. FTIR results indicate that C–S–H formed by the pozzolanic action of bagasse ash differs in its nature from that formed by hydration of OPC, encapsulates Cr(VI) ions and refines the microstructure of hydrated cement pastes as indicated from immobilization efficiency, XRD and SEM results.

► In cement immobilization of Cr(VI), 1.36% wt/wt of K2CrO4 to dry cement was used.
► Addition of Cr(VI) affects the pore formation mechanism of hardened cement pastes.
► Bagasse ash reacts with portlandite of hydrated cement pore giving additional C–S–H.
► C–S–H formed in presence of bagasse ash differs from that formed by hydration of OPC.
► Efficiency of Cr(VI) immobilization was enhanced with up to 15% bagasse ash content.