Khemarath Osathaphan

Effect of pH on transport of Pb2+, Mn2+, Zn2+ and Ni2+ through lateritic soil: Column experiments and transport modeling

This study investigated the effects of pH on the transport of Pb2+, Mn2+, Zn2+ and Ni2+ through lateritic soil columns. Model results by fitting the symmetric breakthrough curves (BTCs) of bromide (Br-) with CXTFIT model suggested that physical non-equilibrium processes were absent in the columns. The heavy metal BTCs were, however, asymmetrical and exhibited a tailing phenomenon, indicating the presence of chemical non-equilibrium processes in the columns. The retardation factors of Pb2+ were the largest of the four metal ions at both pH 4.0 (33.3) and pH 5.0 (35.4). The use of Langmuir isotherm parameters from batch studies with HYDRUS-1D did not predict the BTCs well. Rather the two-site model (TSM) described the heavy metal BTCs better than the equilibrium linear/nonlinear Langmuir model. The fraction of instantaneous sorption sites (f) of all four metal ions on the lateritic soil was consistently about 30%-44% of the total sorption sites.

Competitive sorption and transport of Pb2+, Ni2+, Mn2+, and Zn2+ in lateritic soil columns.

Knowledge of sorption and transport of heavy metals in soils in the presence of other metals is crucial for assessing the environmental risk of these metals. Competitive sorption and transport of four metals, Pb(2+), Ni(2+), Zn(2+), and Mn(2+), were investigated using multi-metal column experiments with lateritic soils obtained from a gold mine impacted by acid mine drainage. Based on Pb(2+) breakthrough time for single-metal system at a pH of approximately 5, the sorption capacity of Pb(2+) was estimated to be higher in lateritic soil than the other metals. For multi-metal systems, the estimated retardation factors for the metals from highest to lowest were: Pb(2+)>Zn(2+)∼ Ni(2+)>Mn(2+), suggesting the mobility of metals through lateritic soil for a multi-metal system would be in the order of Mn(2+)>Ni(2+)∼ Zn(2+)>Pb(2+). For binary and multi-metal systems, the estimated sorption capacities of individual metals were found to be lower than the sorption capacities in single metal system - indicating possible competition for sorption sites. Mass recoveries estimates showed that the sorption of metals was more reversible under competitive multi-metal systems than in single metal systems.

Effect of ethylenediaminetetraacetate on the oxidation of cyanide in an electrochemical process

The effect of ethylenediaminetetraacetate (EDTA) on the removal of cyanide (CN−) from electroplating wastewater was investigated using an electrochemical process. Decay of 100 mg/L CN− was carried out as a function of electrical current (I = 0.5–5.0 A) and molar ratios of EDTA to CN− (2.6–15.7) at pH 13.0. The experiments showed that electrooxidation of CN− follows first-order kinetics with respect to CN− ion. The first-order rate constant, k, showed linearity with the applied current (r2 = 0.99). At a molar ratio of 2.6 ([EDTA]: [CN−]) and electric current, I = 2.5 A, the oxidation of CN− proceeded by a slower rate than in the absence of EDTA. Under similar conditions, the oxidation rate of cyanide increased at molar ratios ranging from 5.2 to 15.7. Consequently, the energy consumption for the electrooxidation of CN− varies with the amount of EDTA present in the solution.

Oxidation of Ni(II)-cyano and Co(III)-cyano complexes by Ferrate(VI): Effect of pH

Free cyanide (CN−) and metal-cyanide complexes (tetracyanonickelate(II)), Ni(CN)42− and hexacyanocobaltate(III)), Co(CN)63- are common constituents of effluents of mining, coal gasification, and petroleum refining. This article presents the degradation of Ni(CN)42− and Co(CN)63- by ferrate(VI) (FeVIO42−, Fe(VI)) in alkaline media. The effect of pH (9.0-11.0) and reactant molar ratios on the degradation of the cyanide complexes was investigated. The removal of Ni(CN)42− ion in 200 min was found to be > 90% at pH 9.0; forming cyanate (NCO−) ions as the stoichiometric products ([Fe(VI)]:[Total CN−] = [Fe(VI)]:[NCO−] ≈ 1.0). The degradation efficiency decreased with an increase in pH from 9.0 to 11.0. Comparatively, the Co(CN)63− ion could be degraded only up to 10% in 200 min at pH 9.0 and the final oxidized products were nitrite and nitrate ions. The oxidation efficiency of removing Co(CN)63− did not vary significantly with pH. Fe(VI) consumptions as a result of the oxidation of free cyanide and metal-cyanides and their products are compared and discussed.