Author: Eng. Tarek Morsy
This study aims to recover valuable metals such as molybdenum and cobalt from spent desulfurization catalyst. Desulfurization techniques of petroleum products, spent catalyst waste management, metals recovery techniques from spent catalysts and the factors affecting the leaching process have been clarified. Experiments were carried out on a spent catalyst produced from hydrotreating unit of naphtha for desulfurization in ANRPC refinery, where the sample was washed with de-ionized water followed by drying at 110 °C. This sample was then roasted in an oxygen-containing gas at 650 °C for removing carbon content, for changing the form of the valuable metals into oxides and removing oil and sulfur components present in small amount in the waste catalyst. The roasted spent catalyst particles were grinded and sieved by means of laboratory sieve to obtain different particle size. A leaching solution of caustic soda was used for molybdenum recovery and another solution of sulfuric acid was used for cobalt recovery. Different variables were studied to clarify their impact on the recovery of metals (molybdenum and cobalt) such as: 1. Concentration of leaching solution ((1-4) M for NaOH and (0.25-1) M for H2SO4). 2. Solid to liquid ratio from (1/10) to (1/100) g/ml 3. Agitation speed from 50 to 250 rpm 4. Particle size from > 850 micro to < 150 micro 5. Temperature from 30 to 80 °C The study indicated that increasing the concentration of caustic soda over 1 molar or increasing the concentration of sulfuric acid over 0.5 molar has no significant positive effect on the percent recovered of molybdenum and cobalt, the decrease in solid to liquid ratio leads to a clear increase in the percent recovered of molybdenum and cobalt, there is an increase in recovery of molybdenum and cobalt by increasing stirring speed, the lower the particle size the higher the percent of molybdenum and cobalt recovered and there is a clear increase in molybdenum and cobalt recovery by increasing temperature.