Eutrophication is the undesired growth of organisms in a confined water body. The most important compound responsible for this phenomenon is phosphate. Phosphates are mainly discharged into water resources from agriculture and fertilizer industries. This study evaluates the potential of raw spent peppermint tea (PM), spent green tea (GT), powdered purple corn cob (PC) and powdered yellow corn cob (YC) as adsorbents of phosphate from aqueous solutions. Batch experiments at room conditions were carried out as a function of pH, adsorbent dose, initial concentration of phosphate and presence of salts and heavy metals. Maximum adsorption capacity was observed at pH 10 with a minimum mass of 50 and 75 mg for YC and PC, respectively. Equilibrium data were fitted to the most important isotherm theories, obtaining a maximum adsorption capacity of 34 and 42 mg/g for YC and PC, respectively, under the Sips, Redlich-Peterson, Temkin and Langmuir mathematical theories. Salts and heavy metal experiments confirmed a strong electrostatic adsorption mechanism for PC and a mixed electrostatics/size affinity for YC. The use of raw PC and YC opens up new alternatives of inexpensive and environment-friendly adsorbents for phosphate.
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