Solidification/Stabilization Of Chromium Contaminated Soil By Alkali Activated Materials

Chromium and its compounds are widely used in leather, printing and dyeing, stainless steel and other industrial production. Lots of chromium contaminated soil were generated, which caused great harm on the ecological environment. And the approach of its harmless disposal and resource utilization is a hot research field.Cr(Ⅵ) and total Cr leaching test and the unconfined compressive strength tests were carried out to study the solidification/stabilization of chromium contaminated soil, using alkali activated slag and alkali activated fly ash materials. XRD. XPS and SEM were used to analysis the mechanism of solidification/stabilization. The results show that:1. For alkali-slag system, increasing the slag content and concentration of alkali appropriately were both helpful for higher strength and lower leaching concentrations of Cr(VI) and total Cr. The increasing of liquid/solid ratio could reduce the leaching concentrations of Cr(VI), although the strength was declined. KOH and sodium silicate were the best combination of alkali activation. Appropriate composition of alkali-slag material of chromium contaminated soil For example, when the soil mixed with 30% slag. KOH and sodium silicate dosage were 8 mol/L and 0.6g/ml. and liquid to solid ratio was 0.2 (L/kg). strength after solidification/stabilization was 22MPa. and the Cr (VI) and total chromium concentrations were 0.05mg/L and 0.1mg/L.2. For alkali-fly ash system the solidification/stabilization was not as well as alkali-slag system. Cr(Ⅵ) leaching concentrations were significantly high. And increasing the curing temperature was effective for both strength and concentration of the leaching. After mixed by FeCH, concentration of Cr (VI) was significantly declined. For example, when the soil mixed with 30% fly ash. curing temperature is 60℃, FeCl2 dosage was 0.02moL strength after solidification/stabilization was 15.8MPa, and the Cr (Ⅵ) and total chromium concentrations were 0.1mg/L and 0.2mg/L.3. Mechanism of alkali-slag and alkali-fly ash-FeCl2 solidification/stabilization of chromium contaminated is mainly reflected in the following two aspects: Enwrapping of the soil particle, and blocking the exudation channel by hydration products. Then reducing Cr (Ⅵ) to Cr (Ⅲ), the less mobility form, which is more likely to be wrapped in the cementitious system. In Alkali-slag system, its cementitious properties come from the formation of C-S-H gel and other hydration products, and the reducibility comes from the presence of ferrous and sulfide and other reducing substances in slag. In alkali-fly ash-FeCh system, its cementitious properties come from the re-aggregate of silicate and aluminum-oxygen, and the reducibility comes from FeCl2.Research in this paper show that alkali-slag and alkali-fly ash-FeCl2 both have the ability of solidification/stabilization chromium contaminated soil effectively. Total chromium and Cr (VI) leaching concentration were low and strength was high, which means it has potential for re-using as low strength building materials that worthy of further study.