Sorption of Boron by Hydrous Al-Oxide

Abstract

Abstract--Boron sorption by hydrous Al-oxide was studied as a function of concentration, pH, temperature and in the presence of oxalate and phosphate. For comparison sorption of B was also measured with charcoal as adsorbent.At constant pH a Langmuir type equation was found to fit the results well at pH values below 7.2 where only boric acid molecules are present in solution. B sorption was dependent on pH with maximum sorption at pH 8.5. Oxalate and phosphate ligands form strong bonds to AI and were found to reduce B sorption. Sorption of boric acid molecules decreased with increasing temperature and the isosteric heat of reaction was 13.8 kJ mol -~. These results indicate that there are two mechanisms of sorption on hydrous Al-oxide, physical sorption of boric acid molecules and ligand exchange (chemisorption) of borate, and both mechanisms are favored onto the oxide.

11B NMR investigation of boron interaction with mineral surfaces: Results for boehmite, silica gel and illite

“…For all three phases, the B-concentration generally increases with increasing pH, and for boehmite and silica gel reaches a maximum at pH 9 and decreases at pH 11. These observations are in agreement with those of previous studies, which show B-sorption maxima at pH 8-9 for clay minerals and aluminum hydroxides (Bloesch et al, 1987;De Bussetti et al, 1995;Goldberg et al, 1996;Prodromou and Thessaloniki, 2000). The reaction BðOHÞ 3 0 þ OH À $ BðOHÞ 4 À has an equilibrium constant log K = 9.2 in aqueous solution at 25°C (Shriver et al, 1994), and the maximum amount of sorption on mineral surfaces occurs ideally at pH = 9.2, (Singh and Mattigod, 1992), in agreement with the observations for silica gel and boehmite here.…”

“…This variation parallels its occurrence in solution as BðOHÞ 3 0 at low pH and BðOHÞ 4 À at high pH (De Bussetti et al, 1995;Suarez, 1995, 1997;Peak et al, 2003). Several sets of adsorption experiments have indicated that B(4) species are preferentially adsorbed from solution relative to B(3) and that they occur as both inner-sphere (ligand-exchanged, chemisorbed) and outer-sphere (physisorbed) complexes on mineral phases including goethite, Al oxide, and clay minerals (Goldberg et al, 1993;Keren et al, 1994;De Bussetti et al, 1995). Isotopic studies also suggest strong adsorption of borate on marine clay and marine carbonates (Palmer et al, 1987;Hemming and Hanson, 1992).…”

“…Sorption isotherm and infrared (IR) spectroscopic studies of high surface area phases such as hydrous aluminum and iron oxide, iron hydroxide, and allophone have shown that boron occurs in both trigonal (B(3)) and tetrahedral (B(4)) coordination on mineral surfaces and that the B(4)/[B(3) + B(4)] ratio increases with increasing pH. This variation parallels its occurrence in solution as BðOHÞ 3 0 at low pH and BðOHÞ 4 À at high pH (De Bussetti et al, 1995;Suarez, 1995, 1997;Peak et al, 2003). Several sets of adsorption experiments have indicated that B(4) species are preferentially adsorbed from solution relative to B(3) and that they occur as both inner-sphere (ligand-exchanged, chemisorbed) and outer-sphere (physisorbed) complexes on mineral phases including goethite, Al oxide, and clay minerals (Goldberg et al, 1993;Keren et al, 1994;De Bussetti et al, 1995).…”

“…Boron adsorption on minerals is affected by many factors including pH, ionic strength, competing ions or organic matter, and the mineral species (De Bussetti et al, 1995;Goldberg et al, 1996Goldberg et al, , 2004Prodromou, 2004). The pH is very important, with maximum B-sorption occurring at pH 8-10 for many phases including goethite, Al oxyhydorxides, and clay minerals (Bloesch et al, 1987;De Bussetti et al, 1995;Goldberg et al, 1996;Prodromou and Thessaloniki, 2000).…”

“…The pH is very important, with maximum B-sorption occurring at pH 8-10 for many phases including goethite, Al oxyhydorxides, and clay minerals (Bloesch et al, 1987;De Bussetti et al, 1995;Goldberg et al, 1996;Prodromou and Thessaloniki, 2000). The presence of other anions and increasing ionic strength generally increase B-sorption (Goldberg et al, 1993(Goldberg et al, , 1996De Bussetti et al, 1995), although the effect of ionic strength is different on different minerals. For example, Goldberg et al (1993) found that boron adsorption increases with increasing ionic strength for montmorillonite, a montmorillonite soil, goethite, kaolinite, a kaolinite soil, but gibbsite.…”