| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 146059 | Chemical Engineering Journal | 2015 | 7 Pages |
•Zn(II) removal by adsorption and coprecipitation with Al(OH)3 was studied.•Zn(II) removal mechanism was mainly surface complexation.•Surface precipitation of Zn–Al LDH partly occurred by coprecipitation.•Quantitative DLM model was constructed for Zn(II) removal with Al(OH)3.
The sorption mechanism of dilute Zn [initial Zn(II) concentration up to 40 mg dm−3] on aluminum hydroxide was investigated. Adsorption and coprecipitation at pH 7 were compared. The adsorption process gave a Langmuir-type isotherm and the zeta potential of Zn(II)-adsorbed aluminum hydroxide decreased linearly with increasing sorption density of Zn on aluminum hydroxide. The adsorption mechanism is therefore mainly surface complexation. In contrast, in the coprecipitation process, a Brunauer–Emmett–Teller like isotherm was obtained; the slope of the zeta potential versus Zn(II) sorption density decreased when the initial Zn/Al molar ratio was greater than 0.5. The X-ray diffraction pattern of Zn(II)-coprecipitated aluminum hydroxide changed from that of poorly crystalline gibbsite to a Zn–Al layered double-hydroxide (LDH) when the initial Zn/Al molar ratio was greater than 0.5, showing that surface complexation was the main sorption mechanism, but surface precipitation of Zn–Al LDH was also involved when the initial Zn/Al molar ratio in the coprecipitation process was greater than 0.5. A quantitative diffuse-layer model was constructed. The aluminum hydroxide exchange capacity was set at 0.61 mol mol-Al−1, based on the experimentally determined surface area, 340 m2 g−1. Surface complexation coefficients for H+, OH−, and Zn(II) adsorption on aluminum hydroxide were determined by fitting to the experimental adsorption results. The obtained parameters were in excellent agreement with those previously reported for a database of gibbsite adsorption equilibrium constants. The pH edge for Zn(II) removal by aluminum hydroxide was successfully reproduced by the constructed model.
