Effects of metal ions and organic ligands on the adsorption of Co(II) onto silicagel

Osaki, Susumu; Kuroki, Yasuhiro; Sugihara, Shinji; Takashima, Yoshimasa

doi:10.1016/0048-9697(90)90214-f

Cited by 10 publications

(1 citation statement)

References 21 publications

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“…For ~x-SiO 2 and silica-gel, with pHpzc values in the range 2 to 3, no evidence of ligand-like adsorption of the chelate or the metal chelate has been observed for equal molar Pb-EDTA and Cu-EDTA (Vuceta 1976), Cu-EDTA (Bourg and Schindler 1979), Ni-EDTA (Bowers 1982) and Co-NTA (Osaki et al 1990). As the chelate-to-metal ratio was increased in these studies, the cation-like adsorption decreased, because the solution chelate competed more effectively with the solid for the metal.…”

Section: Introductionmentioning

confidence: 99%

Adsorption of Nitrilotriacetate (NTA), Co and CoNTA By Gibbsite

Girvin

Gassman

Bolton

1996

Clays and clay miner.

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Abstract--Adsorption of Co 2 § nitrilotriacetic acid (NTA) and equal-molar Co 2 § and NTA by a low surface area (LSA) commercial gibbsite (3.5 m 2 g-~) was investigated in batch as a function of pH (4.5 to 10.5), adsorbate (0.5 to 10 txM) and adsorbent (0.5 to 75 g L ~) concentrations and ionic strength (0.01 to 1 M NaC104). The adsorption of Co 2 § (Co-only) and the acid form of NTA (NTA-only) by gibbsite in 0.01 M NaC104 exhibit cation-like and anion-like adsorption edges, respectively. For the equal-molar CoNTA chelate, Co and NTA adsorption edges were similar but not identical to the Co-only and NTAonly edges. Differences suggest the existence of a ternary CoNTA surface complex with the Co in the intact chelate coordinated to surface hydroxyls. NTA-only adsorption was insensitive to ionic strength variation, indicating weak electrostatic contributions to surface coordination reactions. This is consistent with the formation of inner-sphere surface NTA complexes and ligand exchange reactions in which monodentate, bidentate and binuclear NTA surface complexes form. Cobalt adsorption increases (edge shifts to lower pH by 1 pH unit) on LSA gibbsite as ionic strength increases from 0.01 to 1 M NaC104. For the same ionic strength change, a similar shift in the Co-only edge was observed for another commercial gibbsite (16.8 m 2 g 1); however, no change was observed for ~-A1203. Ionic strength shifts in Co 2+ adsorption by gibbsite were described as an outer-sphere CoOH § surface complex using the triplelayer model. Results suggest that, at waste disposal sites where 6~ and NTA have been co-disposed, NTA will not promote ligand-like adsorption of Co for acid conditions, but will reduce cation-like adsorption for basic conditions. Thus, where gibbsite is the dominant mineral sorbent, NTA will not alter 6~ mobility in acidic pore waters and groundwaters; however, NTA could enhance 6~ mobility where alkaline conditions prevail, unless microbial degradation of the NTA occurs.

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Section: Introductionmentioning

confidence: 99%