Experimental Study on Factors Affecting the Recovery of Nickel from Spent Catalyst

Nickel is widely used as a catalyst in chemical and petrochemical industries. Due to their low cost competing replacements, these are the catalysts of choice in several industries. Such catalysts use silica and alumina as supports [1]. As these catalysts, is used, metals from the feedstock deposit on the internal surface of its pores and its external surface, eventually plugging the pores and decreasing the activity of the catalyst to such an extent it does not give the desired product quality [2]. If the regeneration of these catalysts is not economically feasible, they are discarded from petroleum processing and, at present, large dumps of spent catalysts are growing. Hence, the spent catalysts disposal poses an unavoidable environmental issue, which necessarily requires high capital investment, huge swaths of land and massive efforts [3]. In many countries, the hazardous nature of the spent catalysts is attracting the attention of environmental authorities and the refiners are suffering pressures from them for safe handling of spent catalysts. Several alternative methods such as reclamation of metals, disposal in landfills, utilisation as raw materials to produce other useful products and regeneration and reuse are available to the refiners to deal with the spent catalyst problem. The choice between these options depends on technical feasibility and economic considerations [4]. The recovery methods of nickel from spent catalysts can be classified as thermal treatment, chlorination, acid leaching, alkali leaching, bioleaching. The pyrometallurgy process was applied to the spent catalyst by Llanos et al. [5] who used alkali roasting, and Kim et al. [6] explored a low-temperature sulphuric acid baking and mild acid leaching for maximum dissolution of metal values from a spent NiMO/Al2O3 hydroprocessing catalyst. However, hydrometallurgical process can be regarded as the desired route for recovery of metals due to its economic operation, environmentally friendly and simplicity. Alkaline or acidic leaching was used by many researchers by using many reagents. Marcantonio [7] invented a process to extract valuable metals. In this study, the spent catalyst was roasted at (400-600°C) and then contacted with an aqueous solution of ammonium sulfate ((NH4)2SO4), ammonium carbonate ((NH4)2CO3) and hydrogen peroxide. The optimum leach conditions were 0.5 M (NH4)2SO4, 1 M (NH4)2CO3 and 80°C for three hours was obtained. Angelidis et al. applied a two-step of leaching alkali (sodium hydroxide) followed by acid (sulfuric acid) procedure and studied the selective recovery of metals, such as Mo, Co and Ni, from hydrodesulfurization (MoNi/Al2O3–SiO2 and Mo-Co/Al2O3) catalysts [8]. Al-Mansi and Abdel Monem used sulfuric acid as a solvent to recovery of nickel from the spent catalyst (NiO/Al2O3) resulting from the steam reforming process [9]. It was found that 99% of nickel was extracted at 50% sulfuric acid concentration, particle size less than 500 μm, solid to liquid ratio (1:12) by weight for more than 800 rpm and 5 h at 100°C. Sahu et al. invented a process for nickel and alumina recovery by using 3 vol.% of sulfuric acid with a small amounts of a persulphate salt additives (such as potassium, sodium and ammonium) [10]. It was concluded that as a leaching process is achieved with sulfuric acid alone, the recovery of nickel about 11.95% at 70°C and 4 ml/g after 6 h. High percent of nickel about 99.6% was extracted by using the additives and at 90°C, 1 g of persulphate salt, 4 ml/g liquid to solid ratio and after 1 h. Mulak et al. discussed a method of leaching by using oxalic acid solution with hydrogen peroxide addition [11]. The optimum conditions that give the high extraction of metals 65% Ni, 90% Mo, 33% Al and 94% V was obtained (3 M H2O2 and 0.5 M H2C2O4 solution at 50°C after 4 h). A combined acid-leaching was proposed by Lai et al. to recover valuable metals from spent hydrodesulfurization (HDS) catalyst [12]. An acid solution consisting of concentrated HCl/H2SO4/HNO3 with a volume ratio of 1:1:2 was used to leach the metals. The leaching yields of target metals (Ni, Mo and V) in the 1st stage of leaching reached 99, 90 and 99%, respectively under these conditions, solid to liquid ratio 40 g/l, 1 h leaching time, and 70°C temperature. Oza et al. investigated recovery of nickel from spent nickel catalysts using ultrasonication-assisted nitric acid leaching [13]. The effect on nickel recovery of temperature, solid to liquid (S:L) ratio, time of digestion, and nitric acid concentration were studied in detail and optimized for the ultrasonication route. High purity and faster recovery were accomplished for ultrasonicationassisted leaching than the chelation method (7 h) and conventional acid leaching (9 h). It was found that 95% recovery of nickel was produced Abstract