Examination of the influence of Cr, Ni and Zn on the manufacture and use of cement

The investigations covered not only the influence of high levels of chromiu m, nickel and zinc on pure clinker phases, cement clinker and, cement but a lso the fixation of the heavy metals in hardened cement paste. The results of the investigations show that the heavy metals in natural concentrations- but also at elevated concentrations up to 1,000 ppm-have no measurable infl uence on the burning process and hydration properties. With very strongly i ncreased additions of heavy metals it was possible to detect modification c hanges and formation of new phases in, the unhydrated clinker and pure clin ker phases. Cement hydration is also affected by very high heavy metal conc entrations, at which chromium has an accelerating effect and zinc a retardi ng one. With the exception of chromium the strengths of cement mortars were not detrimentally affected even by extremely high heavy metal additions of 25,000 ppm. Heavy metal fixation was investigated with the aid of a tank t est, the DEV-S4 method and leaching from cements. Regardless of the cement composition and the type of leaching nickel and zinc were so well fixed tha t they could hardly be detected in the eluate. The leachability of the chro mium depended to a greater extent on the cement composition and method of l eaching used.