Indra Perdana

Evaluation of shrinking core model in leaching process of Pomalaa nickel laterite using citric acid as leachant at atmospheric conditions

Most of kinetics studies related to leaching process used shrinking core model to describe physical phenomena of the process. Generally, the model was developed in connection with transport and/or reaction of reactant components. In this study, commonly used internal diffusion controlled shrinking core model was evaluated for leaching process of Pomalaa nickel laterite using citric acid as leachant. Particle size was varied at 60-70, 100-120, -200 meshes, while the operating temperature was kept constant at 358 K, citric acid concentration at 0.1 M, pulp density at 20% w/v and the leaching time was for 120 minutes. Simulation results showed that the shrinking core model was inadequate to closely approach the experimental data. Meanwhile, the experimental data indicated that the leaching process was determined by the mobility of product molecules in the ash layer pores. In case of leaching resulting large product molecules, a mathematical model involving steps of reaction and product diffusion might be appropriate to develop.

Lithium recovery from spent Li-ion batteries using coconut shell activated carbon

Lithium is one of scarce natural resources in the world that need to be preserve. One of the way in preserving the resource is by recovery the rich source of the lithium such as in the spent batteries. It is necessary to develop a recovery method which is efficient and low-cost to be able to recover the lithium in an economic scale. In this study, low-cost activated carbon (AC) from coconut shell charcoal was prepared by chemical and physical activation methods and tested for Li removal from Co, Mn, and Ni ions in semi-continuous columns adsorption experiments. The maximum surface area is 365u202fm2/g with the total pore volume is 0.148u202fcm3/g that can be produced by physical activation at 800u202f°C. In the same activation temperature, activation using KOH has larger ratio of micropore volume than physical activation. Then, the adsorption capacity and selectivity of metal ions were investigated. A very low adsorption capacity of AC for Li ions in batch adsorption mode provides an advantage in column applications for separating Li from other metal ions. The AC sample with chemical activation provided better separation than the samples with physical activation in the column adsorption method. During a certain period of early adsorption (lag time), solution collected from the column outlet was found to be rich in Li due to the fast travel time of this light element, while the other heavier metal ions were mostly retained in the AC bed. The maximum lag time is 97.3u202fmin with AC by KOH activation at 750u202f°C.

Breakdown Voltage of CF3CHCl2 gas an Alternative to SF6 Gas using HV Test and Bonding Energy Methods

For more than two decades of Sulphur Hexafluoride (SF6) gases is used as a gas insulation in high voltage equipment especially in substations. In addition to getting an advantage as an insulating gas. SF6 gas is recognized as one of the greenhouse effect gases that cause global warming. Under the Kyoto Protocol, SF6 gas is one of those gases whose use is restricted and gradually reduced to the presence of a replacement gas for SF6 gas. One of the alternative gas alternatives which have the potential of replacing SF6 gas as an insulating gas in Gas Insulated Switchgear (GIS) equipment in the substation is Dichlorotrifluoroethane (CF3CHCl2) gas. The purpose of this paper is to enable a comparison of breakdown voltage with high voltage test and method of calculating Bonding energy to Dichlorotrifluoroethane gas as substitute gas for SF6 gas. At 0.1 bar gas pressure obtained an average breakdown voltage of 18.68 kV / mm at 25oC chamber temperature and has the highest breakdown voltage at 50oC with a breakdown voltage of 19.56 kV / mm. The CF3CHCl2 gas has great potential as an insulating gas because it has more insulation ability high of SF6 gas, and is part of the gas recommended under the Kyoto Protocol. Gas CF3CHCl2 has the capacity to double the value of electronegativity greater than SF6 gas as a major requirement of gas isolation and has a value of Global Warming Potential (GWP) and Ozone Depleting lower than from SF6 gas.