硅酸盐水泥硬化体中Cr的存在形态分析

CHEMICAL FORM OF Cr EXISTING IN HARDENED PORTLAND CEMENT

采用改进的BCR(TheCommunity Bureauof Reference)分级浸提方法对硅酸盐水泥硬化体进行分离,并利用离子色谱、紫外–可见分光光度计等测定浸提液中离子浓度,利用X射线衍射和差热分析对浸提剂处理后残渣的组成进行分析,以研究改进的BCR分级浸提方法对硅酸盐水泥硬化体的分离作用以及水泥硬化体中Cr的存在形态与分布。结果表明:所选取的3种浸提剂能够有效地分离水泥水化产物,区分其中不同结合形态的Cr。硅酸盐水泥硬化体中Cr的存在形态可划分为:酸可交换态Cr、可还原态Cr、可氧化态和残渣态Cr,其中,酸可交换态Cr含量低于0.5%;可还原态Cr约占1%,其受环境pH值的影响较大;可氧化态和残渣态为水泥硬化体中Cr的主要存在形态,约为98%。随着龄期的延长,酸可交换态Cr会逐渐向残渣态转换,向环境溶出的可能性减小。

The aim of this work is to study the adaptability of BCR （The Community Bureau of Reference） sequential extraction procedures, proposed by the Commission of the European Community Bureau of Reference, to the extraction of hardened Portland cement and the analysits of chemical form and distribution of Cr existing in it. Four solutions and three residues were obtained through three-step extraction tests carried out on hardened Portland cement using the BCR method, and then they were analyzed with ion chromatography, spectrophotometry, ultraviolet and visible spectrophotometry, X-ray diffraction and thermo gravimetry-differential scanning calorimetry. The results show that： （1） The BCR sequential extraction procedure can be used to selectively dissolve phases in hydrated Portland cement and analyze the chemical form of Cr in it. （2） Cr in hardened Portland cement exists in the following four forms： acidic exchangeable form, reducible form, oxidizable and residue form （indissoluble form）. Of these, the indissoluble form is a dominant fraction, accounting for beyond 98% of the total amount of Cr by mass in hardened Portland cement. The acidic exchangeable form and reducible form only account for 0.5% and 1%. （3） The Cr of the exchangeable form is changed to the residual form gradually with curing time, which is favorable for the immobilization of Cr in hardened cement.