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The adsorption efficiency of a biomass by-product (cactus fibres) regarding the removal of copper(II) from aqueous solutions has been investigated before and after its chemical treatment. The chemical treatment of the biomass by-product included phosphorylation and MnO2-coating. The separation/removal efficiency has been studied as a function of pH, Cu(II) concentration, ionic strength, temperature and contact time. Evaluation of the experimental data shows that the MnO2-coated product presents the highest adsorption capacity, followed by the non-treated and phosphorylated material. Regarding the effect of ionic strength/salinity on the adsorption, in contrast to the removal efficiency of the phosphorylated product, which is significantly affected, the MnO2-coated and non-treated material don't show any effect, indicating the formation of inner-sphere surface complexes. The adsorption reaction is in all cases endothermic and relatively fast, particularly the adsorption on the MnO2-coated product. The results of the present study indicate that for the removal of bivalent metal-ions from contaminated waters the MnO2-coated material is expected to be the most effective adsorbent and an alternative to MnO2 resins for the treatment of environmentally relevant waters.

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