Nickel retention by goethite and hematite

Nickel adsorption by variable charge soils: effect of pH and ionic strength

“…This occurred in a particular form in the Oxisols samples and in the lower pH value range (3-5). In this situation, the pH value was much below the zero point of salt effect (ZPSE) of the predominant mineralogical constituents of the Oxisols, especially hematite, goethite and amorphous (oxy)hydroxides (Beukes et al, 2000). Metallic ion adsorption by positively charged surfaces is insensitive to the alterations in the ionic strength (Kosmulski, 1997).…”

“…Many adsorption studies with mineral soils have shown increase in Ni adsorption with increase in pH (Harter, 1983;Elzinga and Sparks, 2001). Harter (1983) and Beukes et al (2000) reported that metal adsorption was pH-dependent and that the intensity of the phenomenon increased drastically above pH 7.0. Practically all the Ni added (5 mg L -1 ) disappeared from the soil solution when the pH was over 7.0, regardless of soil or sampling depth.…”

“…If it is accepted that electrostatic attraction is the predominant mechanism, it seems reasonable to accept the hypothesis that, in the case of Ni adsorption, the effect of the pH is more critical in determining the adsorbent surface charge and not the metal species in solution due to their action in hydrolysis. Positive charges of the Ni ions are less repulsed when the pH reaches values close to the zero point of salt effect of oxide minerals such as goethite (8.5) and hematite (9.2) (Beukes et al, 2000). As general concluding remarks, chemical and mineralogical soil attributes should always be considered as criteria for selecting the areas for disposal or application of residues containing Ni to minimize soil contamination and impact on the environment.…”

“…This aspect is of particular interest for Ni adsorption, because there is no consensus yet on its retention mechanism by the soil. Nickel adsorption has been studied in pure systems, such as Fe, Al and Mn hydrated oxides (McKenzie, 1980;Beukes et al, 2000), clay minerals (Mattigod et al, 1979;Echeverría et al, 2003;Sen Gupta and Bhattacharyya, 2006) and organic matter (Mellis et al, 2004), and in complex systems such as the soil, under natural and agricultural conditions or with residue application (Camargo et al, 1989;Pombo et al, 1989;Mellis et al, 2004;Iglesias et al, 2007). However, sufficient data have not yet been gathered on Ni adsorption by weathered soils of the wet tropics to assure the implementation of efficient prevention techniques and remediation of soil contamination.…”

Cr(VI) Generation During Flaring of CO-Rich Off-Gas from Closed Ferrochromium Submerged Arc Furnaces

“…Atmospheric SO 2 can dissolve in moisture, which can result in Cr(VI) reduction. [26,27] Therefore, as a precautionary measure, the received ore samples were dried in desiccators prior to further use.…”