2005 Volume 12 Issue 314 Pages 3-11
As a result of examination on the Cr (VI) immobilization behavior of calcium aluminoferrites, the following results were obtained. Each type of calcium aluminoferrites sorbs Cr (VI) in liquid phase according to the hydration. The Cr (VI) decreasing rate of calcium aluminoferrites is larger than that of OPC or BB, and its immobilization capacity is also large. According to estimation of Cr immobilization capacity per gram of various calcium aluminoferrites, the capacities of C6A2F and C4AF are 109 mg·g-1 and 101 mg·-1 respectively. When calcium aluminoferrites sorbed Cr according to the hydration, they took Cr into the hydrated products in the form of Cr (VI) as it was before. Formation of CrO42- type U-phase was confirmed in a case of high Cr concentration. This phenomenon was supposedly caused by the follows : (1) the main component of the Cr standard solution was K2Cr2O7, (2) both concentrations of alkali metal ions (K, Na) and CrO42- were high by the addition of NaOH for adjusting pH to neutral state. Compared with calcium silicate, OPC and BB, calcium aluminoferrites are resistant to the leaching of Cr (VI) that was sorbed by the hydration, which leads to excellent immobilizing ability for Cr (VI).
