Adsorption oxide minerals

Kampf N, Scheinost AC, Schultze DG (2000) Oxides minerals. In Sumner ME (ed) Handbook of soil science, CRC Press, Boca Raton (FL), F125-F168 Jain A, Loeppert RH (2000) Effect of competing anions on the adsorption of arsenate and arsenite by ferrihydrite. J Environ Qual 29 1422-1430 Jain A, Raven KP, Loeppert RH (1999) Arsenite and arsenate adsorption on ferrihydrite surface charge reduction and net OH release stoichiometry. Environ Sci Technol 33 1179-1184... 

Several reactions between constituents in As-contaminated groundwater and oxic sediments controlled As mobility in the laboratory experiments. Adsorption was the primary mechanism for removing As from solution. The adsorption capacity of the oxic sediments was a function of the concentration and oxidation state of As, and the concentration of other solutes that competed for adsorption sites. Although As(lll) was the dominant oxidation state in contaminated groundwater, data from the laboratory experiments showed that As(lll) was oxidized to As(V) by manganese oxide minerals that are present in the oxic sediment. Phosphate in contaminated groundwater caused a substantial decrease in As(V) adsorption. Silica, bicarbonate and pH caused only a small decrease in As adsorption. 

Even if the solubility limit of relevant solid phases is not exceeded, a large fraction of trace metals in natural waters often occurs bound to particles of various size ranges (nanometres to millimetres). An important process for binding of metals to particles is adsorption to mineral surfaces (often oxides or hydroxides) [29]. 

The Heterogeneous Case. Hachiya et al. (1984) and Hayes and Leckie (1986) used the pressure-jump relaxation method to study the adsorption kinetics of metal ions to oxide minerals. Their results support in essence the same adsorption mechanism as that given for homogeneous complex formation. 

Goldberg, S., and G. Sposito (1984), "A Chemical Model of Phosphate Adsorption by Soils I. Reference Oxide Minerals II. Noncalcareous Soils", Soil Sd. Soc. Am. 48, 772-783. 

Goldberg, S. Sposito, G. (1984) A chemical model of phosphate adsorption by soils. I. Reference oxide minerals. Soil Sci. Soc. Am. J. 48 772-778... 

Kraemer, S.M. Hering, J.G. (1997) Influence of solution saturation state on the kinetics of ligand-controlled dissolution of oxide phases. Geochim. Cosmochim. Acta 61 2855-2866 Kraemer, S.M., Xu, J., Raymond, K.N. Spo-sito, G. (2002) Adsorption of Pb(II) and Eu(III) by oxide minerals in the presence of natural and synthetic hydroxamate sidero-phores. Environ. Sd. Technol. 36 1287-1291 Kraemer, S.M. Cheah, S.-F. Zapf, R. Xu, J. Raymond, KN. Sposito, G. (1999) Effect of hydroxamate siderophores on Fe release and Pb(II) adsorption by goefhite. Geochim. Cosmochim. Acta 63 3003—3008 Kratohvil, S. Matijevic, E. (1987) Preparation and properties of coated uniform colloidal partides. I. Aluminum (hydrous) oxide on hematite, diromia, and titania. Adv Ceram. Mater. 2 798-803... 

Manning, B.A. Goldberg, S. (1996) Modeling competitive adsorption of arsenate with phosphate and molybdate on oxide minerals. Soil Sci. Soc. Am. J. 60 121-131 Manning, B.A. Fendorf S.E. Goldberg, S. (1998) Surface structures and stability of ar-senic(lll) on goethite spectroscopic evidence for inner-sphere complexes. Environ. Sci. Techn. 34 2383-2388... 

Adsorption to mineral surfaces such as Fe and Al (hydr)oxides has long been known to be an important process that limits the mobility of heavy metals and metalloid species in aqueous systems (e.g., Stumm 1992). The sorption of ionic species in MSWI bottom ash has been recently studied in detail by Meima Comans (1998, 1999). These authors used a sequence of selective chemical extractions to determine sorbent concentration, namely Fe and Al (hydr)oxides. Their model calculations suggested that Zn(II) and M0O4 sorbed to Fe (hydr)oxides, while Pb(II) and Cu(II) appeared to have a greater affinity for Fe (hydr)oxides. The sorption of Cd(Il) was found to be very weak. The interpretation of... 

A number of attempts have been made to understand the mechanism of the adsorption of chelates on oxide minerals. For instance, IR spectroscopic studies10 have indicated the presence of a basic monosalicylaldoximate copper complex as well as the bis-salicylaldoximate complex on the surface of malachite (basic copper carbonate) treated with salicylaldoxime. However, other workers4 have shown that the copper chelate is partitioned between the surface and dispersed within the solution, and that a dissolution-precipitation process is responsible for the formation of the chelate. Research into the chemistry of the interaction of chelating collectors with mineral surfaces is still in its infancy, and it can be expected that future developments will depend on a better understanding of the surface coordination chemistry involved. 

Figure 2.7 Stern (inner sphere and outer sphere) and Gouy arsenic adsorption complexes associated with the surfaces of iron oxide minerals.

We observed from the column data that uranium in solution is not very mobile when the solution contacts the sediments used in the experiment. We expected that the oxidized uranium [U(VI)] in the pregnant lixiviant would be reduced and immobilized by solu-tion/sediment interactions, and this is what happened in the experiments after two to three pore volumes were eluted. The actual removal of uranium from solution may occur by adsorption onto mineral surfaces, which produces localized high concentra-... 

FIGURE 7.5 Pb adsorption of biogenic Mn oxide compared to that of colloidal Fe oxyhy-droxide and abiotic Mn oxide minerals (pyrolusite). (From Nelson, Y.M. et al., Appl. Environ. Microbiol., 65, 175, 1999b. With permission.)... 

In the surface complexation model, Stumm and co-workers (Furrer and Stumm, 1983, 1986 Stumm and Furrer, 1987 Stumm and Wieland, 1990) suggested that adsorption or desorption of protons on an oxide surface polarizes the metal-oxygen bonds, weakening the bonding between the cation and the underlying lattice and explaining the pH-dependence of rates. Surface complexation reactions for an oxide mineral can be written as follows (Schindler, 1981) ... 

In practice, however, it seems that much of the Hg contained within soils and weathered rock is more or less firmly associated with solid phases. This can be shown to extend from simple sorption to structural incorporation within oxidate minerals. The manner of the association between Hg and organic matter has been discussed by Jonasson (1970). The question of adsorption is a rather grey area and, whilst it is clear that it plays a very significant role in soil experiments (e.g., Andersson, 1979), it seems that in mature soils the Hg is held rather more firmly. (This is apart from discrete mineral hosts deriving from sulphide oxidation.) It is possible that, as a simple adsorbent ages, the associated Hg may enter the structure, becoming a "residual" element effectively removed from the dynamic weathering cycle. 

Goldberg, S., 1986, Chemical modeling of arsenate adsorption on aluminum and iron oxide minerals Soil Science Society of AmeiicaJournal, v. 50, p. 1154-1157. 

To evaluate the predominant pH effect on the kinetics of reductive dissolution of oxide minerals, it is indispensable to examine the pH dependence of both the rate, R, and the overall rate constant, ka, of reductive dissolution. The rate constant differs from the rate by the surface concentration of the reductant, R = ka RedadJ. If the rate constant ka is independent of pH, then the pH dependence of the rate is solely due to the pH dependence of adsorption of the reductant at the (hydr)oxide surface. If, on the contrary, the rate constant is dependent on pH, then other pH effects have to be considered. 

---