Selenium(VI) removal from caustic solution by synthetic Ca–Al–Cl layered double hydroxides

To extract selenium(VI) from the highly caustic leachate of copper anode slime, the Ca–Al–Cl layered double hydroxides (Ca–Al–Cl–LDHs) with a formula of Ca2Al(OH)6Cl·2H2O by three co-precipitation methods were synthesized. A plate-like morphology and hexagonal crystal structure with typical mineral phases and functional groups were identified by the FESEM, XRD, FTIR, BET and XPS analysis. The forward feeding sample exhibits the best adsorption capacity of Se(VI). The factor experiments then reveal a favorable adsorption process with low temperature, low NaOH concentration and high adsorbent dosage. Furthermore, the adsorption kinetics and isotherm parameters can be well described by the Langmuir isotherm and the pseudo-second-order models, respectively. Accordingly, the maximum adsorption amount of Se(VI) onto Ca–Al–Cl–LDHs reaches 188.6 mg/g at 50 °C.