Waste to valuable by product - utilization of carbonised decanter cake from palm oil milling plant as an effective adsorbent for heavy metal ions in aqueous solution

摘要

Palm oil milling plant generates large amount of waste that was proven to causeudenvironmental problems. About 40 kg decanter cake was generated from each ton ofudfresh fruit bunch processed. Previous studies suggested agricultural waste could beudemployed as heavy metal ion adsorbent. Due to the similarity of decanter cake withudother agricultural waste we proposed to explore the use of decanter cake as an adsorbentudfor heavy metal ion removal.udUtilization of decanter cake as an effective adsorbent for Cd 2 , Cu2 and Pb2 ionudremoval from aqueous solution has been studied. The decanter cake was first dried atud105 °C and then carbonized at various temperatures. The resulting carbonized decanterudcake were tested for removing Cd2 , Cu 7+ and Pb2 ions. Proximate analysis usingudthermogravimetry analysis of decanter cake carbonized at 500 °C indicated that theudadsorbent contained 4% moisture, 21% volatile,23% fixed carbon, and 52% ash.udAdsorption test were normally carried out by mixing 1.0 g of the decanter cake in 100udmL aqueous solution of the various ions. The concentration of metal ions in theudsolutions used is in the range of 100 - 1000 mg/t.udThe results of adsorption studies indicated that the removal of metal ions wasudhighest in the case of Pb2 when the carbonization temperature was 500 °C and 600 °Cudin the case of Cd2 and Cu2 . Maximum removal of the Cd2 , Cu2 and Pb2 were alsoudobserved to take place when the pH of the solution is in the range of 4 - 5. Langmuirudand Freundlich isotherm models were used to fit the isotherm experimental data. Theudmaximum uptakes of Cd2 , Cu2 and Pb2 onto the carbonized decanter cake in thisudstudy were estimated to be 24, 23, and 97 mg/g respectively. Adsorbed metal ions canudbe desorbed from adsorbent using dilute HC1 solution. The adsorption kinetics wasudfound to follow the pseudo-second-order kinetic model. Thermodynamic parametersudsuch as standard enthalpy (MI"), standard entropy (AS-) and Gibbs free energy (AG-)udwere determined. Adsorption process was endothermic and had negative value of Gibbsudfree energy changes. The competitive adsorption characteristics of binary and ternaryudheavy metal ions Cd2 , Cu2 and Pb2 on PDC500 were investigated in batch systems.udEquilibrium adsorption data showed that PDC500 displays a high selectivity toward oneudmetal in two-component or a three-component system with an affinity order of Pb2>udCu2 > Cd2 Chemical activation of decanter cake using ZnC12 increased the maximumudadsorption capacity for Cd2 , Cu2 and Pb2 significantly to 52, 44, and 159 mg/gudrespectively. Kinetic and thermodynamic properties of adsorption were affected byudchemical activation.udScale up of the batch process into industrial scale was explored using theudLangmuir parameter from experimental data. A three-stage continuous counter currentudadsorption unit gave the best adsorption performance for Pb2 ion removal in term ofudminimum adsorbent consumption.