A green desilication method from highly concentrated chromate solutions by Mg-Al-CO3 LDH

Abstract

The Mg-Al-CO3 LDH was synthesized as a desilication agent to effectively and environmentally remove Si(IV) from Na2CrO4-NaAlO2-NaVO3-Na2SiO3-H2O solutions. It was observed that the changes of reaction parameters including temperature, NaOH concentration, time, the dosage of Mg-Al-CO3 LDH and NaAlO2 concentration significantly affected the desilication efficiency, while the effect of Cr(Ⅵ) and V(Ⅴ) concentration on the desilication was negligible. The results showed that 91.5% Si(IV) could be removed after desilication at 90 °C for 6 h with the additive of 4 g/L Mg-Al-CO3 LDH, without the formation of hazardous Cr(VI)-containing compounds. It could be concluded that the desilication mechanism was dominated by the synergistic effect between the ion exchange of Si(IV) and the formation of zeolite compounds. The method proposed in this study provides a new insight for Si(IV) removal from the highly concentrated Cr(VI) solutions in the chromate clean production.