Preparation and evaluation of the Ca-Al layered double hydroxide for removal of copper(II), nickel(II), zinc(II), chromium(VI) and phosphate from aqueous solutions

Hydrocalumite (CaAl-LDH) was prepared by the co-precipitation method with different Ca2+/Al3+ molar ratios. Hydrocalumite at the molar ratio of 4:1 Ca2+/Al3+ (4HC) showed to be efficient in the removal of Cu2+, Ni2+ or Zn2+ from the aqueous solution. The products formed between 4HC and the Cu2+, Ni2+ or Zn2+ cations were characterized by atomic absorption, SEM, XRD and IR. The effect of several factors such as pH, dose, contact time and metal concentration were evaluated. The maximum removal capacity was 7.0 mmol g−1 for Cu2+ and Ni2+, and 6.3 mmol g−1 for Zn2+. X-ray diffraction analyses showed that the products formed were CuAl, NiAl and ZnAl LDHs. The 4HC also was applied for removal of metal cations and the oxyanions Cr(VI) or phosphate from the same solution. In solutions containing 400 mg L−1 of Cu2+, Ni2+ or Zn2+ and 200 mg L−1 of Cr(VI) or phosphate (expressed as phosphorus), and in the presence of 1 g L−1 of 4HC, 100% of the metals and 60, 57 and 52% of Cr (VI) or 93, 80 and 92% of phosphate were removed, respectively. The results showed that 4HC has great potential to be used in the treatment of effluents containing metal cations and oxyanions.