Powdered nanolimestone (NLS) and limestone (LS) have been investigated as an adsorbent for the removal of cobalt from aqueous solutions. Batch experiments were carried out to investigate the effect of pH. The favorable pH for maximum cobalt adsorption was 6.8. The surface area increased in the case of NLS up to 6.2 m2/g, while it was equal to 0.5 m2/g in the case of LS. The adsorption capacity calculated by the Langmuir equation was 17.1 mg/g for LS and 60.0 mg/g for NLS at pH 6.8. The adsorption capacity increased with temperature and the kinetics followed a first-order rate equation. The enthalpy change (ΔHo) was 20.8 Jmol−1 for LS and 41.6 Jmol−1 for NLS, while entropy change (ΔSo) was 33.3 JK−1 mol−1 for LS and 74.8 JK−1 mol−1 for NLS, which substantiates the endothermic and spontaneous nature of the cobalt adsorption process. All of the results suggested that the NLS is very strong and could be an excellent nano-adsorbent for cobalt contaminated water treatment more than limestone.

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