Specific Adsorption of Copper on an Hydroxy-Aluminum-Montmorillonite Complex
1984
Harsh, J. B. | Doner, H. E.
The adsorption of Na on a prepared hydroxy-aluminum-montmorillonite complex (OH-Al-SWy-l) was investigated as a function of pH, time, and Cu concentration ([Cu]). It was found that Na adsorption from 0.01M NaClO₄ increased with pH from 0.015 mol kg⁻¹ at pH 4.5 to 0.33 mol (Na⁺) kg⁻¹ clay at pH 6.6 Adsorption of 0.16 mol (1/2 Cu²⁺) kg⁻¹ clay did not affect the amount of Na adsorption, showing that specific sites existed for Cu. Adsorption of Cu was found to increase with pH and both adsorption and resistance to extraction with 0.25M Ba(NO₃)₂ increased with time. At pH 4.6, Cu adsorption approached a maximum near 0.3 mol (1/2 Cu²⁺) kg⁻¹ clay of which 0.13 mol (1/2 Cu²⁺) were extracted with Ba(NO₃)₂. Electron spin resonance (ESR) of the Cu on OH-Al-SWy-l showed that both physi- and chemisorbed Cu were present and that solubilization as Cu(NH₃)²⁺₄ through exposure to NH₃ vapor overnight was possible only if the sample had been previously treated with BaCl₂. It was concluded that the OH-Al-SWy-l system provided a much more reactive surface toward Cu adsorption than either montmorillonite or hydrous aluminum oxides. In comparison to smectites Cu was less labile to Ba extraction due, in part, to chemisorption by Al-OH groups. Relative to values reported for Al(OH)₃ polymorphs, Alₓ(OH)y³ˣ⁻ʸ precipitated in the presence of montmorillonite adsorbed more Cu on a mass basis presumably due to a higher surface to mass ratio.
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