Distribution of Cr,As and Pb in cement mortar determined by electron probe microanalysis

Clinker and cement mortar were produced from raw materials with Cr,As and Pb by simulating the high-temperature calcination in a cement kiln.According to the electron probe microanalysis (EPMA) point,line and surface analysis,the distribution and mineral phases of Cr,As and Pb in cement paste and concrete were identified and the microphysicochemical species of Cr,As and Pb were characterized,thus establishing a theoretical basis to understand the release mechanisms of Cr,As and Pb in cement paste.The results show that:Cr was predominantly enriched in the calcium silicate hydrates,whose content decreases gradually from the center of the gel to the circumference.Other mineral phases,including portlandite crystal and middle phases,with lower content,and some Cr grains with high concentration of Cr exist in the gel.In the cement mortar,only the calcium silicate hydrates contained As,the content in other mineral phases being nearly zero,and the majority of As is likely to form arsenate on the surface of hydration products in the form of physical fixation or sorption.The distribution of Pb in the cement mortar was highly decentralized.A low level of Pb was present in every hydration product,the calcium silicate hydrates being an exception with a somewhat higher Pb content.A large portion of Pb probably forms some compounds with other elements dispersed on the surface of each hydration product.