The Chemical Role of Cement and Lime in the Stabilization Mechanisms of Lead Contaminated Iraqi Soils

Unfortunately, Iraq has wide areas of heavy metals contaminated lands due to mismanagement of activities dealing with these pollutants. But, Iraq is one of the biggest countries in the Middle East in the production of cement and lime and both are of low prices and available in the local markets as building materials. This study is designed to investigate the use of (0.0, 3.0, 6.0 and 9.0% by weight) hydrated lime “locally known as Nora” and Portland cement in the treatment of many lead contaminated Iraqi soil samples and then studying their role in soil stabilization; as measured by a newly developed “mini” JET device and by the dispersion ratio method (DR, %) determined in 1:2 soil: water solutions. The results revealed that both lime and cement can significantly improve the stability of these soils and only 6% of both stabilizers were required to get the optimum soil stabilization. According to the “mini” JET calculations of the critical shear stress (?c, pa) and the erodibility coefficient (kd), by using a linear model and the Blaisdell solution technique, both stabilizers have improved the soil engineering properties that are related to soil stabilization. Thus, stabilizers have reduced both the scouring depth (SD) and the erodibility coefficient (kd) of treated soils. The DR values in both stabilizers were highly correlated with the (kd) coefficients (R= 0.99 and 0.94 in lime and cement, respectively) and the soil solution chemistry, which is the main concern of this study, was of prime important in this respect. Chemically, both stabilizers have increased pH (from 7.18 to 9.20, R= 0.98 for lime; from 7.18 to 8.65, R= 0.97 for cement) but decreased both EC (from 3.50 to 1.40 mS/cm, R= -0.82 for lime; from 3.50 to 1.30 mS/cm, R= -0.85 for cement) and SAR (from 6.30 to 1.98, R= -0.96 for lime; from 6.3 to 2.8, R= -0.85 for cement) in treated soil solutions. Concerning the pH changes, lime has more impact than cement in increasing pH, especially in higher additions (i.e. 9%, pH 9.20 in lime, and 8.65 in cement ), and this may make lime as being less efficient than cement as a stabilizer. However, both stabilizers have successfully decreased the erodibility coefficient (kd, from 1090 to 170 cm3/kN.s, R= -0.78 in lime, and from 1090 to 0.0 cm3/kN.s, R= -0.85 in cement) and the dispersion ratio (DR, from 7.03 to 1.96%, R= -0.83 in lime, and from 7.03 to 1.33%, R= -0.96 in cement) and hence the lead solubility (Pb, from 48.8 to 19.5 ppm, R= -0.96 in lime, and from 48.8 to 12.2 ppm, R= -0.84 in cement) in the solutions of lead contaminated soil. Cement, with no doubt, was more efficient than lime in this respect.