Abstract
The adsorption of manganese ions from aqueous solutions by pure and acid-treated Opuntia ficus indica as natural low-cost and eco-friendly adsorbents was investigated. The adsorbents' structures were characterized by powder X-ray diffraction and infrared spectroscopy. Specific surface areas were determined using the Brunauer-Emmett-Tell equation. The study was carried out under various parameters influencing the manganese removal efficiency such as pH, temperature, contact time, adsorbent dose and initial concentration of manganese ion. The maximum adsorption capacity reached 42.02 mg/g for acid-treated Opuntia ficus indica, and only 20.8 mg /g for pure Opuntia ficus indica. The Langmuir, Freundlich and Temkin isotherms equations were tested, and the best fit was obtained by the Langmuir model for both adsorbents. The thermodynamic study shows that chemisorption is the main adsorption mechanism for the activated adsorbent while physisorption is the main adsorption mechanism for the pure adsorbent. The kinetics of the adsorption have been studied using four kinetics models of pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion. Structural analyses indicate the appearance of MnOx oxides on the cellulose fibers. The adsorption mechanisms consist of an electrostatic interaction followed by oxidation of the Mn (II) to higher degrees, then probably by binding to the surface of the adsorbent by different C-O-MnOx bonds.
Highlights
Unlike organic pollutants, which are mostly affected by biological degradation, the hazards of heavy metals are related to their inability to degrade into non-harmful end products
Manganese adsorption onto Opuntia Ficus Indica Powder (OFIP) and Ac-OFIP was investigated as a function of solution pH, adsorbent dosage, initial concentration of Mn (II) and temperature
A very high percentage of manganese elimination has been observed in the case of Ac-OFIP
Summary
Unlike organic pollutants, which are mostly affected by biological degradation, the hazards of heavy metals are related to their inability to degrade into non-harmful end products. It can cause acute and chronic damage to various organisms if present. Manganese (Mn) is the third most abundant transition metal in nature, usually present in surface water and groundwater as a divalent ion (Mn2+). The Mn (IV) precipitate can stain utensils and clothing,[8] and gives water an unpleasant metallic taste and odor, an increased turbidity and a biofouling of pipelines.[2,9]
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