Bioleaching of nickel from spent petroleum catalyst using Acidithiobacillus thiooxidans DSM-11478.

The present work deals with optimization of culture conditions and process parameters for bioleaching of spent petroleum catalyst collected from a petroleum refinery. The efficacy of Ni bioleaching from spent petroleum catalyst was determined using pure culture of Acidithiobacillus thiooxidans DSM-11478. The culture conditions of pH, temperature and headspace volume to media volume ratio were optimized. EDX analysis was done to confirm the presence of Ni in the spent catalyst after roasting it to decoke its surface. The optimum temperature for A. thiooxidans DSM-11478 growth was found to be 32 °C. The enhanced recovery of nickel at very low pH was attributed to the higher acidic strength of sulfuric acid produced in the culture medium by the bacterium. During the bioleaching process, 89% of the Ni present in the catalyst waste could be successfully recovered in optimized conditions. This environment friendly bioleaching process proved efficient than the chemical method. Taking leads from the lab scale results, bioleaching in larger volumes (1, 5 and 10 L) was also performed to provide guidelines for taking up this technology for in situ industrial waste management.

Flocculation of Cu, Mn, Ni, Pb, and Zn during estuarine mixing [Caspian Sea]

During estuarine mixing of fresh water with saline water and due to the flocculation process, a portion of dissolved metals come into particulate phase, and the dissolved load decreases. This process plays an important role in self-purification of heavy metals in rivers. In this study, flocculation of Cu, Mn, Ni, Pb and Zn during mixing of Cheshme-Kileh River water with Caspian Sea water has been investigated. Salinity and electrical conductivity are the governing factors for the flocculation of Mn and Cu. Zn and Ni are governed by pH. Dissolved oxygen is a governing factor for the flocculation of Pb. Rapid flocculation occurs in the earlier stages of mixing. The final flocculation rates of metals are in the following order: Mn [68.79%] > Pb [45.45%] > Ni [26.32%] > Cu [23.08%] > Zn [21.21%]. In addition, electro-flocculation [EF] is investigated. The results reveal that EF had adverse effect on flocculation rates of heavy metals. General pattern of EF of metals is like the following: Mn [57.89%] > Pb [40.9%] > Cu [23.08% > Ni [22.37%] > Zn [15.15%]. Furthermore, the effect of decreasing pH level on flocculation of heavy metals is studied. Except for Mn, decreasing the pH increased the flocculation rates of heavy metals. Maximum flocculation of Ni, Cu, Pb, and Zn occur at pH about 7.5. Due to the flocculation of trace metals during the estuarine mixing about 51.6, 7.8, 5.5, 3.9, and 3.6 ton/year of Mn, Ni, Zn, Pb, and Cu, respectively, are removed from the river water

Removal of nickel ions from industrial plating effluents using activated alumina as adsorbent.

Removal of nickel ions from industrial effluents has been studied using activated alumina prepared by the galvanic oxidation of aluminum metal at ambient temperature as the adsorbent. The effect of various factors, such as initial concentration of nickel, contact time, dose of adsorbent and pH of the solution has been investigated. Batch and column type of adsorption studies have been made. The results indicate that the adsorption process is favored at pH 9. The adsorption data were fitted with suitable adsorption isotherm. The optimum conditions for the best adsorption have been evaluated for the following factors: dosage, contact time, pH, initial concentration of nickel ions and temperature. The process of regeneration of the adsorbent has also been studied.

Mechanism of extraction of Fe [III], Fe [II], Co [II] and Ni [II] by Di- [2-ethylhexyl] phosphoric acid from sulphuric acid medium

Distribution ratio, D, for iron, cobalt and nickel as a function of acidity and extractant molarity has been determined in a sulphate-di [2-ethylhexyl] phosphoric acid [DEHPA] system using benzene or 2-ehtyl hexanol as non polar and polar diluents respectively. The extractability of Fe [III] by DEHPA in benzene goes through a minimum with increasing acidity of the aqueous phase. The divalent ions Fe [II], Co [II] and Ni [II] seem to be poorly extracted at low acidities [0.5-IM] with the formation of M [HX2]. On the other hand, Fe [III] exhibited the highest value of D suggesting of its separation from these divalent ions With 2-ethyl hexanol, the distribution ratio for all ions are lower than in benzene and the extraction proceeds through chelate formation of Fex3 or MX2 for Fe [II], Ni [II] and Co [II].