Acid activation pine cone waste at differences temperature and selective removal of Pb²⁺ ions in water

This study reports potential application of pine cones (PC) and acids treated pine cone at as adsorbents for removal of Pb²⁺ ions in water. Two different types of acids were used for the treatment of PC at different activation temperature, with the following combination of hydrochloric -acid treated PC at 25 °C (PC-H25) and 50 °C (PC-H50); phosphoric-acid treatmented PC at 25 °C (PC-P25) and 50 °C (PC-P50). The basic physicochemical properties of PC, both before and after acid treatment, were characterized using scanning electron microscopy (SEM), Fourier-transformed infrared spectroscopy (FTIR) and elemental analysis (EA). Bath adsorption experiments on Pb²⁺ ions were optimized in term of pH, adsorbent dose, reaction time and initial concentration of Pb²⁺ ions. It was estimated through adsorption isotherm analysis that adsorption capacities of PC-H25, PC-P25, PC-H50 and PC-P50 on Pb²⁺ ions were 132.6, 108.2, 148.3 and 119.8 mg/g, respectively. Desorption studies revealed the promising regeneration potential of PC, PC-H25, PC-H50, PC-P25 and PC-P50. It was found that the percentage removal of Pb²⁺ was maintained at more than 60% as compared to the initial value, even after 5 adsorption-desorption cycles. Furthermore, the adsorption costs required for removal of Pb²⁺ ions using PC, PC-P25, PC-P50, PC-H25, PC-H50 were estimated to be 1.6, 11.5, 17.5, 6.7 and 8 US$/kg, respectively. Based on these findings, PC and acid-treated PC could be used as low-cost, eco-friendly and effective adsorbents for the Pb²⁺ removal from water.