Keywords: fly ash, hexagon chromium leakage, oxide magnesium, MgO additive, batch contact test, column percolation test, clay minerals, Cr(VI) concentration
Effect of MGO additive on preventing leakage of Cr(VI)
The effect of a new additive, oxide magnesium (MgO), on preventing or reducing the leakage of Cr(VI) from a fly ash (coal ash) has been investigated by batch contact and column percolation tests. The test results indirectly indicate that the MgO additive has an obvious effect on reducing Cr(VI) to Cr(III), which is less environmentally hazardous. However, the process of reducing Cr(VI) to Cr(III) may be reversible because adding H2SO4 or CaH2O2 into the balanced solid–liquid mixture for partially simulating possible environmental change increased Cr(VI) concentration in the liquid phase. Adding 10% to 30% of Ariake clay into the fly ash not only further reduced Cr(VI) concentration, but also reduced total Cr concentration. Hence, Cr(III) ions may be absorbed by the clay minerals. For the conditions investigated, the column percolation test resulted in higher initial Cr(VI) concentration in the liquid phase than that of the batch contact test. Further, the results of the column percolation test using the samples with different curing time (up to three weeks) indicate that with MgO additive, curing the sample does not have an obvious effect on Cr(VI) concentration.