Effects of pyrolysis conditions on the porous structure development of date pits activated carbon

Activated carbons were prepared from biomass of Algerian date pits for developing efficient and cheap adsorbents in the aim to remove heavy metals from waste water. Carbon adsorbents were obtained following two successive treatments: pyrolysis under dry nitrogen flow and physical activation under wet nitrogen flow. Pyrolysis process was optimized by varying some operating parameters such as temperature, nitrogen flow, heating rate and pyrolysis hold time in order to determine their effects on the porous structure development of date pits activated carbon. Chars obtained from pyrolysis process were activated with the same operating conditions (activation temperature of 700 °C, 50% nitrogen + 50% water flow rate of 150 cm3/min and heating rate of 10 °C/min) except for the activation hold time which varied from 0.5 to 4 h. Experimental results showed that pyrolysis conditions have significant effects on the chars and activated carbons properties prepared from date pits. The best microporous activated carbon (surface area of 464 m2/g, microporous volume of 0.203 cm3/g and total pore volume of 0.220 cm3/g) was obtained by pyrolysis at 10 °C/min up to 700 °C for 1 h under 150 cm3/min of nitrogen. Activation hold time has also an impact on activated carbons porosity. The best surface area, microporous volume and total pore volume were obtained after activation for 4 h: 1467 m2/g, 0.711 cm3/g and 0.725 cm3/g respectively. The best adsorbents prepared from date pits were then tested for the removal of Fe3+ and Cu2+ from aqueous solutions. Results show that these adsorbents have higher metallic cation adsorption capacities than usual commercial activated carbons because of the presence of both carboxylic and phenolic groups at the surface witch improves the cation-exchange and complexation properties of these adsorbents in addition of the greater specific surface area. Adsorption data were analyzed with Langmuir and Freundlich isotherms. The better fit is obtained with the Langmuir model.