P L. Smedley, D.G. Kinniburgh/ Applied Geochemistry 17(2002 )517-568 535 Studies of As adsorption by metal oxides Mineral Reference Ghosh and Yuan(1987) inetics, column breakthrough. Regeneration by desorbing with NaoH Modelling with pH-dependent Langmuir isotherm(for As)and surface complexation model (for protons) aluminium hydroxide As(V)on precipitated Al(OH)3(pH 3-10). 'Adsorption'exceeded Amorphous Anderson et al. (1976) HFO Kinetics and pH dependence of As(V) and As(lll) adsorption on HFO Raven et al. (1998) (202 m2g-l) Found very high As( V) and As(llD) loadings(up to 4-5 mol As k )at the highest concentrations. pH adsorption envelopes at various AsT loadings HFO or ars d arsenate over free concentration Pierce and Moore(1982) ge from 10-7to 10-3M(pH 4-10). Fitted to Langmuir isotherm at concentrations and linear isotherm at higher concentration Dzombak and Morel(1990)fitted this data to their diffuse double Sorption of As(V) and As(ln) on HFO at As concentrations of Wilkie and Hering(1996) environmental significance (low micromolar range)and pH 4-9. with Dzombak and Morel (1990)model predictions- generally reasonable agreement. SO4 decreased adsorption of As(V) and As(lll), especially at low pH, while Ca increased As(V)adsorption high pH. I mM bicarbonate did not affect either As(V)or As(lln) adsorption greatly HFO A wide angle X-ray scattering(and EXAFS) study of two-line Waychunas et al. (1996) rrihydrite coprecipitated with varying amounts of As(V) suggest hat the As reduced crystallite size because of the formation of stror bound inner sphere complex between As(V) and edge sharing Fe(o,oH) octahedra Saturation at As/Fe mol ratio of 0.68 HFO As(In)and As(V)adsorption and OH- release/uptake on synthetic two-line Jain et al. (1999) ferrihydrite. As(V) at pH 9.2 released up to I mol OH" per mol As sorbed whereas As(llD) released <0.25 mol As per mol Fe. At pH 4.6, OH-release as much less for As(V) adsorption and under these conditions there was a net release of H+ by arsenite. These differences reflect the mechanism of As adsorption and influence the pH dependence of adsorption Granular "ferric hydro n in the sub-uM concentration range: SO4 comp Driehaus et al. (1998) significant at mM concentrations below pH 7 only; phosphate compe at'natural groundwater concentrations Goethite An EXAFS and XANES study of As(Ill) adsorption to a synthetic goethite Manning et al.(1998) uggested bidentate inner sphere binding. One plot of As(Ill) and As(V)pH adsorption envelopes As(lln) data fitted to Constant Capacitance SCM Goethite Matis et al. (1997) or As Shows pH edge at about pH 9. Data fitted Langmuir isotherm presumably at constant pH(up to 60 mg I-I As) Goethite Successfully applied the CD-MUSIC surface complexation model to literature data for anion adsorption to goethite including As(V)-P (1999) ompetition. The CD-MUSIC is the most promising of the SCMs for modelling complex natural systems Goethite As(V) adsorption on synthetic goethite primarily for a study of impact latis et al. (1999) on flocculation and electrokinetics. No isotherms. Final pH varied bu not defined (continued on next page)Table 5 Studies of As adsorption by metal oxides Mineral Comment Reference Aluminium oxides As(V) and As(III) adsorption on activated alumina: pH dependence, kinetics, column breakthrough. Regeneration by desorbing with NaOH. Modelling with pH-dependent Langmuir isotherm (for As) and surface complexation model (for protons) Ghosh and Yuan (1987) ‘Amorphous’ aluminium hydroxide As(V) on precipitated Al(OH)3 (pH 3–10). ‘Adsorption’ exceeded 15 mol kg
1 at pH 5. Fitted data to pH dependent Langmuir isotherm Anderson et al. (1976) HFO Kinetics and pH dependence of As(V) and As(III) adsorption on HFO (202 m2 g
1 ). Found very high As(V) and As(III) loadings (up to 4–5 mol As kg
1 ) at the highest concentrations. pH adsorption envelopes at various AsT loadings Raven et al. (1998) HFO Adsorption isotherms for arsenite and arsenate over free concentration range from 10
7 to 10
3 M (pH 4–10). Fitted to Langmuir isotherm at low concentrations and linear isotherm at higher concentrations. Dzombak and Morel (1990) fitted this data to their diffuse double layer model Pierce and Moore (1982) HFO Sorption of As(V) and As(III) on HFO at As concentrations of environmental significance (low micromolar range) and pH 4–9. Compared results with Dzombak and Morel (1990) model predictions— generally reasonable agreement. SO4 decreased adsorption of As(V) and As(III), especially at low pH, while Ca increased As(V) adsorption at high pH. 1mM bicarbonate did not affect either As(V) or As(III) adsorption greatly Wilkie and Hering (1996) HFO A wide angle X-ray scattering (and EXAFS) study of two-line ferrihydrite coprecipitated with varying amounts of As(V) suggested that the As reduced crystallite size because of the formation of strongly bound inner sphere complex between As(V) and edge sharing Fe(O,OH)6 octahedra. Saturation at As/Fe mol ratio of 0.68 Waychunas et al. (1996) HFO As(III) and As(V) adsorption and OH
release/uptake on synthetic two-line ferrihydrite. As(V) at pH 9.2 released up to 1mol OH- per mol As sorbed whereas As(III) released <0.25 mol As per mol Fe. At pH 4.6, OH
release was much less for As(V) adsorption and under these conditions there was a net release of H+ by arsenite. These differences reflect the mechanism of As adsorption and influence the pH dependence of adsorption Jain et al. (1999) Granular ‘ferric hydroxide’ (akageneite) As(V) isotherms given in the sub-mM concentration range; SO4 competition significant at mM concentrations below pH 7 only; phosphate competition at ‘natural’ groundwater concentrations Driehaus et al. (1998) Goethite An EXAFS and XANES study of As(III) adsorption to a synthetic goethite suggested bidentate inner sphere binding. One plot of As(III) and As(V) pH adsorption envelopes. As(III) data fitted to Constant Capacitance SCM Manning et al. (1998) Goethite Batch adsorption of As(V) on synthetic goethite. Used Mo blue analysis for As. Shows pH edge at about pH 9. Data fitted Langmuir isotherm presumably at constant pH (up to 60 mg l
1 As) Matis et al. (1997) Goethite Successfully applied the CD-MUSIC surface complexation model to literature data for anion adsorption to goethite including As(V)-P competition. The CD-MUSIC is the most promising of the SCMs for modelling complex natural systems Hiemstra and van Riemsdijk (1999) Goethite As(V) adsorption on synthetic goethite primarily for a study of impact on flocculation and electrokinetics. No isotherms. Final pH varied but not defined Matis et al. (1999) (continued on next page) P.L. Smedley, D.G. Kinniburgh / Applied Geochemistry 17 (2002) 517–568 535