基于亚硝酸根插层LDHs的高效水泥降铬剂研究

High Efficiency Chromium Reducing Agent for Cement Based on Nitrite Intercalated LDHs

基于层状双氢氧化物(LDHs)结构可重建性,制备亚硝酸根插层的LDHs。将亚硝酸根插层的LDHs作为新型降铬外加剂掺入水泥,研究LDHs降铬效率、耐存储性和球磨温度处理条件下的稳定性,并揭示其还原和固化水泥中可溶性Cr^(6+)的作用机理。结果表明,与水拌和后LDHs-NO_(2)层间释放的亚硝酸根离子能够快速还原水泥中的Cr^(6+),有效降低可溶性Cr^(6+)含量。掺入0.2%(质量分数)LDHs-NO_(2)可使水泥中可溶性Cr^(6+)含量从40.26 mg/kg降至9.36 mg/kg,同时水泥3 d抗压强度增加约2 MPa。还原后的Cr^(3+)与层板中的Al^(3+)进行离子交换进入LDHs层板,从而实现稳定的化学固化。亚硝酸根插层LDHs的还原效率优于FeSO_(4)·7H_(2)O,并且在长时间储存和球磨温度处理条件下仍能保持优异的还原能力。

Based on the structural reconstruction ability of layered double hydroxides(LDHs),the nitrite intercalated LDHs were prepared.In this paper,nitrite intercalated LDHs was added into cement as a new type of chromium reducing admixture.Reduction efficiency,resistance to storage and stability under ball milling temperature conditions of nitrite intercalated LDHs were investigated.The mechanism of reduction and solidification of soluble Cr^(6+)in cement using nitrite intercalated LDHs was revealed.The results show that nitrite ions released from LDHs-NO_(2)interlayer mixing with water rapidly reduce soluble Cr^(6+)and effectively decrease soluble Cr^(6+)content in cement.The addition of 0.2%(mass fraction)LDHs-NO_(2)reduces the soluble Cr^(6+)content in cement from 40.26 mg/kg to 9.36 mg/kg,and improves the compressive strength of cement by about 2 MPa.The reduced Cr^(3+)exchanges with Al^(3+)into LDHs laminate to achieve stable chemical solidification.The reduction efficiency of synthetic nitrite intercalated LDHs is better than FeSO_(4)·7H_(2)O.Furthermore,synthetic nitrite intercalated LDHs remains reductive stability when the cement is stored for a period and treated at ball mill temperature.