The utilization of environmentally benign diluent of palm oil in the supported liquid membrane (SLM) process is able to reduce both environmental and economic problems due to the consumption of the petroleum-based diluent. A preliminary study has been conducted on the removal of nickel ion via SLM using bis(2-ethylhexyl) phosphate (D2EHPA), octanol, kerosene and sulfuric acid solution as a carrier, synergist, diluent and stripping agent, respectively. Several process variables involve namely D2EHPA, octanol and sulfuric acid concentration as well as feed flowrate were optimized using the Box-Behnken design (BBD). Results showed that about 90 and 95% of the nickel ions were successfully removed and recovered, respectively after 6 h at a permeation coefficient of 6.94 x 10(-6) cms(-1) under optimum conditions of 1.25M D2EHPA, 15% (v/v) octanol, 1.75M sulfuric acid and 100 mL/min of feed flowrate. Using the aforementioned optimum condition, a further investigation on the removal and recovery performance of nickel has been carried out by means of the palm oil as a diluent. Interestingly, the result showed that about 91 and 65% of the nickel ions were successfully removed and recovered, respectively. Hence, it revealed that palm oil has high prospective as a substitute for sustainable diluent in the SLM process as well as offering a better insight in the separation process that deals with an environmentally friendly materials in the future. Besides, the stability of the membrane was found to be satisfactory over ten consecutive cycles of operation. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.