Mobilization of zinc, lead, and chromium from soil using chemical oxidants : hydrogen peroxide and potassium permanganate

Experiments were conducted to determine the mobilization of zinc, lead, and chromium using hydrogen peroxide or potassium permanganate on Hanford (sandy) and Portsmouth (clay) soils. The soils utilized are under consideration for remediation by the DOE for removal of organic contaminants by oxidation with hydrogen peroxide or potassium permanganate. The effect of the two oxidants (hydrogen peroxide and potassium permanganate) on mobilization of three metals (Zn(II), Pb(II), and Cr(III)) from two soils (Hanford and Portsmouth) are the subject of this investigation. The two soils are evaluated in three fashions: untreated, pretreated with hydrogen peroxide, and pretreated with potassium permanganate. A time of 48 hours was found sufficient to establish equilibrium between soil and solute. The maximum adsorption capacities (q_max) and binding value (‘b’) for zinc and chromium were estimated from single reciprocal plots of the Langmuir isotherm for the two soils. Linear adsorption isotherms were used for lead with the two soils. The maximum adsorption capacity (q_max) of Zn(II) soils increased after peroxide or permanganate pretreatment of the two soils. The Zn(II) binding (‘b’) values to soil were relatively unaffected by oxidation pretreatment of Hanford soil but decreased with the Portsmouth soil. The distribution coefficient, K_d, for Pb(II) and the two soils increased with peroxide and permanganate pretreatment. For Cr(III), adsorption isotherms could not be obtained for peroxide or permanganate pretreated soil because these soils converted some of the metal ion to Cr(VI) which is poorly sorbed to soil. The adsorption of metal to soil decreased in the order: Cr(III) > Pb(II) ∼ Zn(II). Batch type (rapid mixing) metal mobilization experiments were performed with peroxide and permanganate with the two soils contaminated with the three metals. Metal mobilization experiments were also performed with water alone as a reference. For water alone with the two soils, the mobility decreased in the order; Zn > Pb ∼ Cr. For peroxide solutions with untreated and pretreated soils, the mobility decreased in the order: Cr >> Zn > Pb. For permanganate solutions with untreated and pretreated soils, the mobility decreased in the order: Cr >> Zn > Pb. Column experiments were performed to determine metal mobilization. In column experiments mass transfer rates were smaller than for batch experiments. The low permeability of the Portsmouth soil did not allow its use in column experiments. Water alone showed no detectable metal mobilization. For peroxide solutions with Hanford soil, the mobility decreased in the order Cr >> Zn > Pb. For permanganate solutions with Hanford soil, the mobility decreased in the order: Cr >> Zn > Pb. For peroxide solutions, increasing the flow rate increased the mobilization of Cr. For permanganate solutions, increasing the flow rate decreased the mobilization of Cr. The most mobile metal with water was zinc, whereas lead and chromium were not detectable in aqueous solutions. Hydrogen peroxide and potassium permanganate solutions mobilized the most chromium (30% to 95%). Hydrogen peroxide and potassium permanganate solutions mobilized some zinc (0.2% to 4%), while producing no detectable lead mobilization.