Zinc plant residue is a hazardous waste which contains high quantity of nickel and other valuable metals. Process parameters such as reaction time, acid concentration, solid-liquid ratio, particle size, stirring speed and temperature for nickel extraction from this waste were optimized using factorial design. Main effects and their interactions were obtained by the analysis of variance ANOVA. Empirical regression model was obtained and used to predict nickel extraction with satisfactory results and to describe the relationship between the predicted results and the experiment results. The important parameters for maximizing nickel extraction were identifi ed to be a leaching time solid-liquid ratio and acid concentration. It was found that above 90% of nickel could be extracted in optimum conditions.

Solidification/Stabilization (S/S) method with cement as a binder to remediate metals in petroleum sludge has been successfully proven. However, this technique has not yet been explored to remediate organic contaminants since a high concentration of Total Petroleum Hydrocarbon (TPH) was also detected in the sludge. This study focuses on remediating 16 Polycyclic Aromatic Hydrocarbons (PAHs) compounds in raw petroleum sludge with Portland cement as a binder using the S/S method. The initial concentration of 16 PAHs in the raw sludge was first measured before the performance of the S/S method to remediate the PAHs were evaluated. The S/S matrices were tested for leaching behavior and strength after 7 and 28 days by air curing. The leaching test was measured using the Toxicity Characteristics Leaching Procedure (TCLP), and the remaining PAHs concentration in the matrices was analyzed using a Gas Chromatography-Mass Spectrometer (GC-MS). In the raw sludge, all 16 PAHs compounds were below the standard limit except for Benzo(a)anthracene, Benzo(a)pyrene, Dibenzo(ah)anthracene, and Indeno(1,2,3- cd_ pyrene), which are considered as high rings PAHs. The high rings PAHs show lower concentration in leachate than low rings PAHs, which indicates the potential of the S/S method in remediating high rings PAHs. The high sludge ratio in S/S matrices has shown that the percentage strength is increasing, similar to Portland cement. Therefore, this study contributed to the possibility of the S/S method in the remediation of PAHs in petroleum sludge by using only Portland cement as a binder.