This study explored the potential of Acacia mangium to remediate arsenic present in mine wastes and to determine the remediation mechanism of this plant for removing arsenic. A preliminary test using soil spiked with various arsenic concentrations showed that Acacia mangium was able to survive on arsenic‐contaminated soil with concentrations up to 500 mg kg−1 arsenic. Ex situ phytoremediation studies using mine wastes containing approximately 790 mg kg−1 arsenic also showed no toxicity effect on Acacia mangium throughout 5 months of treatment. Bioconcentration and translocation factors indicate that Acacia mangium utilizes phytostabilization as its main mechanism to uptake arsenic into the plant tissues. The use of the chemical lixiviants monoammonium phosphate and citric acid was also found to increase the translocation of arsenic from roots to stems of Acacia mangium with a 12‐ and six‐fold increase, respectively, compared with the un‐dosed plants. Further speciation analysis revealed that arsenic in the form of arsenate was the only arsenic species detected in the stems after being amended with monoammonium phosphate; thereby, suggesting a sensible strategy for more efficient targeted arsenic phytoremediation by Acacia mangium.

The production of propylene from propane dehydrogenation process in the petrochemical sector regularly produce high concentration of sulphur in the form of sodium sulphide (Na2S). High concentration of sulphide can lead to corrosion in sewage pipes, massive fish kill and obnoxious odors into the atmosphere. Adsorption technique using lowcost and environmentally friendly adsorbents derived from natural resources such as rice husk ash (RHA) may offer a suitable alternative for in situ removal of contaminants such as sodium sulphide in industrial wastewater. In this work, the use of silica synthesized from RHA was investigated for its potential in removing high concentration of sulphide (S 2-) in the form of sodium sulphide from wastewater. Results showed that pure silica with the size around 0.9 to 2.0 μm was successfully synthesized from RHA. Significant reduction of sulphide level was observed after being treated with RHAbased silica calcined with clay compared to other adsorbents such as chemically treated nanoporous zeolite and natural clay itself with more than 90 % removal after 120 minutes of treatment with the value of the pseudo-first-order rate constant, k of 0.1404, 0.14 and 0.1519 for silica compared to zeolite. This suggests that the use of silica derived from RHA has a potential to be used as sulphide remover in industrial wastewater without extensive chemical treatment to improve its removal capacity.