High surface area peat moss biochar and its potential for Chromium metal adsorption from aqueous solutions

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Activated carbons (ACs) have been synthesized using local peat moss biomass for adsorption of heavy metal ions. Adsorbents with different surface areas and pore sizes were obtained using a chemical activation route with different impregnation ratios (20%, 30%, and 40%) of phosphoric acid. The carbonization process was carried out in a tubular furnace under flow of nitrogen (N2) at 500 °C, and 600 °C. Physicochemical properties of developed activated carbon have been evaluated by several techniques such as; X-ray diffraction, Scanning Electron Microscopic, Energy Dispersive X-ray Spectroscopy, Nitrogen adsorption isotherm, Pore size distribution analysis, and Fourier-transform analysis. Moreover, adsorption of chromium ions (Cr+2) from an aqueous solution under different variables was carried out. Heavy metal concentration (20 - 200) ppm, the dosage of adsorbent (0.1 – 0.5) g/L, the time of contact (0 - 220) min, and initial pH (2 - 8) were studied. Results showed that a synthesis route by chemical activation with 30% H3PO4 concentration at 600 °C for 3 h gave the highest BET surface area and pore volume (1692.6 m2/g and 1.55 cm3/g) respectively, compared with other prepared samples. As well as, the removal results show that the maximum adsorption capacity was 493.3 mg/g at 200 mg/L of initial heavy metal concentration, 6.5 pH, 0.3 g/L activated carbon dosage, and 180 min contact time. The Freundlich isotherm was the better description of the adsorption equilibrium data, while the pseudo-second-order model shows the most accurately describes of adsorption kinetics, which indicates that chemisorption is dominant in the adsorption process. Temperature and thermodynamics parameters were studied. The positive value of enthalpy indicates that the adsorption was endothermic.