Preparation of Cement Mixture from Chromium-containing Steel Slag

Steel slag is an industrial waste,and the efficient utilization of steel slag has important environmental value.In this paper,steel slag was used to treat wastewater containing Cr³⁺ and then used as cement mixture.The effect of steel slag adsorbing Cr³⁺ was discussed.The influence of steel slag containing chromium on setting time and fluidity of cement mortar were studied,and the effect of steel slag on strength and hydration performance of cement products was investigated too.The mechanism of cement solidifying Cr³⁺ was analyzed.The results showed that steel slag could effectively dispose of wastewater containing Cr³⁺.When the Cr³⁺ concentration and pH of the wastewater were 40 mg/L and 6,respectively,and the liquid-solid ratio was 10∶1,the adsorption capacity and adsorption rate of Cr³⁺ on the steel slag reached 5.93 mg/g and 85.63%,respectively.The introduction of chromium-containing steel slag improved the fluidity of cement mortar,but reduced the compressive strength of products.The initial setting time,the final setting time and fluidity of cement mortar were 176 min,286 min and 193.2% respectively,when 32 % chromium-containing steel slag was added.The compressive strengths of cement products could reach 42.5 R grade after curing for 7 days and 28 days.XRD and SEM analysis displayed that the low hydration activity of steel slag and the addition of steel slag were not conducive to hydration products formation such as C-S-H gels and tobermorite.Cr³⁺ did not react with other components in the raw material,and its cementation by amorphous calcium silicate hydrate was the main reason to inhibit its leaching activity.Under acidic condition,the Cr³⁺ leaching concentration meet the requirement by GB5085.3—2007 standard.This study provides a new way for the efficient utilization of heavy metal adsorption steel slag.