Debaraj Mishra

Bioleaching kinetics and multivariate analysis of spent petroleum catalyst dissolution using two acidophiles

Bioleaching studies were conducted to evaluate the recovery of metal values from waste petroleum catalyst using two different acidophilic microorganisms, Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. Various leaching parameters such as contact time, pH, oxidant concentration, pulp densities, particle size, and temperature were studied in detail. Activation energy was evaluated from Arrhenius equation and values for Ni, V and Mo were calculated in case of both the acidophiles. In both cases, the dissolution kinetics of Mo was lower than those of V and Ni. The lower dissolution kinetics may have been due to the formation of a sulfur product layer, refractoriness of MoS(2) or both. Multivariate statistical data were presented to interpret the leaching data in the present case. The significance of the leaching parameters was derived through principle component analysis and multi linear regression analyses for both iron and sulfur oxidizing bacteria.

Microbial leaching of metals from solid industrial wastes

Biotechnological applications for metal recovery have played a greater role in recovery of valuable metals from low grade sulfide minerals from the beginning of the middle era till the end of the twentieth century. With depletion of ore/minerals and implementation of stricter environmental rules, microbiological applications for metal recovery have been shifted towards solid industrial wastes. Due to certain restrictions in conventional processes, use of microbes has garnered increased attention. The process is environmentally-friendly, economical and cost-effective. The major microorganisms in recovery of heavy metals are acidophiles that thrive at acidic pH ranging from 2.0–4.0. These microbes aid in dissolving metals by secreting inorganic and organic acids into aqueous media. Some of the well-known acidophilic bacteria such as Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Leptospirillum ferrooxidans and Sulfolobus spp. are well-studied for bioleaching activity, whereas, fungal species like Penicillium spp. and Aspergillus niger have been thoroughly studied for the same process. This mini-review focuses on the acidophilic microbial diversity and application of those microorganisms toward solid industrial wastes.

Arsenic(V) adsorption mechanism using kaolinite, montmorillonite and illite from aqueous medium

The present work investigates the adsorptive behavior of As(V) ions with kaolinite, montmorillonite and illite in aqueous medium as a function of As(V) concentration, pH, contact time and temperature. As(V) adsorption on studied clays were pH dependent and maximum adsorption were achieved in the pH range 2.0–5.0. The adsorption data gave good fits with Langmuir isotherm and yielded Langmuir monolayer capacity of 0.86, 0.64 and 0.52 mg As(V) /g of kaolinite, montmorillonite and illite, respectively. An increase in adsorption temperature resulted in a decrease in the amount of As(V) adsorbed. The results of leaching study showed that, kaolinite was very active clay constituent regarding both As(V) adsorption and mobility. The electrokinetic behavior of both the kaolinite and montmorillonite were modified in the presence of As(V). The shift in isoelectric point indicated that adsorption involves inner sphere surface complexation and strong specific ion adsorption. Kaolinite was successfully tested as an adsorbent for the removal of arsenic from two contaminated groundwater samples containing arsenic in the range 1.36–1.41 mg/L.

Dissolution kinetics of spent petroleum catalyst using sulfur oxidizing acidophilic microorganisms

Bioleaching studies of spent petroleum catalyst were carried out using sulfur oxidizing, Acidithiobacillus species. Leaching studies were carried out in two-stage, in the first stage bacteria were grown and culture filtrate was used in the second stage for leaching purpose. XRD analysis of spent petroleum catalyst showed oxides of V, Fe and Al and sulfides of Mo and Ni. The leaching kinetics followed dual rate, initial faster followed by slower rate and equilibrium could be achieved within 7 days. The leaching rate of Ni and V were high compared to Mo. The low Mo leaching rate may be either due to formation of impervious sulfur layer or refractoriness of sulfides or both. The leaching kinetics followed 1st order rate. Using leaching kinetics, rate equations for dissolution process for different metal ions were evaluated. The rate determining step observed to be pore diffusion controlled.

Bioleaching: A microbial process of metal recovery; A review

The present review describes the historical development and mechanisms of bioleaching. Recent development has shown commercial application of the process and, concurrently, details pertaining to the key microorganisms involved in these processes have been described. Bioleaching of metal sulfides is caused by diverse groups of bacteria. The dissolution biochemistry signifies two types of pathways, which are specifically determined by the acid-solubility of the sulfides, the thiosulfate and polysulfate pathways. This sulfide dissolution can be affected by ‘direct’ and ‘indirect’ mechanisms. In the ‘indirect’ mechanism bacteria oxidize only dissolved iron (II) ions to iron (III) ions and the latter can then attack metal sulfides and then be reduced to iron (II) ions. The ‘direct’ mechanism requires the attachment of bacteria to the sulfide surfaces. In the case of thiobacilli, bacteria secrete exopolymer that facilitates attachment of the bacteria to a metal surface, thus enhancing the leaching rate. In terms of eco-friendliness and process economics, within the field of biohydrometallurgy the technology is considered robust.

Adsorption kinetics of natural dissolved organic matter and its impact on arsenic(V) leachability from arsenic-loaded ferrihydrite and Al-ferrihydrite

The present work was broadly divided into two parts: first, the efficiency of synthetically prepared ferrihydrite and Al-ferrihydrite to adsorb dissolved organic matter (DOM) was tested as a function of time, pH and ionic strength and its effects on specific surface area was found. In the second part, the effect of DOM concentration and solution pH was studied to elucidate the influence of this two parameters on As(V) leachability from As(V) loaded ferrihydrite and Al-ferrihydrite. It was found that both pH and ionic strength had significant influence on DOM adsorption. The behavior and magnitude of adsorption was significantly different for both the materials. In general, the efficiency of Al-ferrihydrite to adsorb DOM was better compared to ferrihydrite. Results indicated that ligand exchange was the dominant interaction mechanism for DOM adsorption on ferrihydrite and Al-ferrihydrite. The study also suggested a strong potential for DOM to mobilize As(V) from the studied materials. At pH 5.0, DOM concentrations of 2.5 and 5.0 mg C/L had negligible effect on As(V) leachability. With increasing DOM concentration from 10 to 30 mg C/L, increased the As(V) leachability into the solution. Net release from ferrihydrite was up to 1.07 mg/g (5.75%) of the total adsorbed arsenic. The corresponding figure for Al-ferrihydrite was 1.47 mg/g (6.30%). As the primary mechanisms for the arsenic release from solid phases we identified two different types of mechanisms i.e., dissolution of the solid phase and competition between arsenic and organic anions for sorption sites.

Removal of Arsenic from Arsenic Rich Sludge by Volatilization Using Anaerobic Microorganisms Treated with Cow Dung

The microbial mediated volatilization of arsenic by anaerobic digestion method was studied using cultures of methanogenic bacteria. Cow dung was utilized as the major substrate for the bacterial growth during arsenic volatilization. Effect of contact time showed that arsenic volatilization followed a linear kinetics up to 40 days and thereafter the kinetics was negligible. Arsenic volatilization was fitted to 1st order plot and the reaction rate constant “k” calculated to be 0. 0282 mg/L/day. The regeneration time of the bacteria was found to be 53.3 hour. The effect of substrate (cow dung) was studied to measure the arsenic volatilization and it was observed that substrate concentration of 25 g/L could volatilize about 35% of arsenic. However, higher substrate concentration decreased arsenic volatilization rate, which may be due to formation of methane that inhibits higher doses of arsenic and led to the formation of non-volatile compounds. The maximum uptake was found to be 1.08 mg of As(V)/g of substrate. The effects of different organic acids on arsenic mobilization have been discussed.

Production of medium-chain-length polyhydroxyalkanoates by activated sludge enriched under periodic feeding with nonanoic acid.

The potential use of activated sludge for the production of medium-chain-length polyhydroxyalkanoates (MCL-PHAs) was investigated. The enrichment of bacterial populations capable of producing MCL-PHAs was achieved by periodic feeding with nonanoic acid in a sequencing batch reactor (SBR). Denaturing gradient gel electrophoresis analysis revealed Pseudomonas aeruginosa strains to be predominant in the bacterial community during the SBR process. The composition of PHA synthesized by the enriched biomass from nonanoic acid consisted of a large concentration (>89 mol%) of MCL monomer units and a small amount of short-chain-length monomer units. Under fed-batch fermentation with continuous feeding of nonanoic acid at a flow rate of 0.225 g/L/h and a C/N ratio of 40, a maximum PHA content of 48.6% dry cell weight and a conversion yield (Y(p/s)) of 0.94 g/g were achieved. These results indicate that MCL-PHA production by activated sludge is a promising alternative to typical pure culture approaches.

A novel process to treat spent petroleum catalyst using sulfur-oxidizing lithotrophs

A novel process was developed using sulfur-oxidizing bacteria to extract metal values like Ni, V and Mo from spent petroleum catalyst. Bacteria were grown in elemental sulfur media for five day and after filtering, the filtrate was used for leaching purpose. Effect of different parameters such as contact time, particle size, pulp density and lixiviant composition were studied to find out the extent of metal leaching during the leaching process. XRD analysis proved the existence of V in oxide form, Ni in sulfide form, Mo both in oxide as well as sulfide forms, and sulfur in elemental state only. In all the cases studied Ni and V showed higher leaching efficiency compared to Mo. The low Mo leaching rate may be either due to formation of impervious sulfur layer or refractoriness of sulfides or both. Leaching kinetics followed dual rate, initial faster followed by slower. Dissolution mechanism was explained on the basis of both surface and pore diffusion rate. The leaching kinetics followed 1st order reaction rate. Finally, multiple linear regression analysis was carried out to compare the observed and calculated leaching percentage values for three metals.

An investigation into the prospects of arsenic(v) removal from contaminated groundwater using untreated bauxite ore.

Steady-state experiments were conducted on arsenic (V) removal from contaminated groundwater using two different grades of bauxite ore. The materials considered were refractory grade bauxite (RB) with high alumina and low iron content and feed bauxite (FB) with moderate alumina and high iron content. Adsorption studies were carried out for different parameters such as pH, adsorbent dosage, As(V) concentration and reaction time to establish optimum conditions. RB was found to be the better adsorbent compared to FB with a maximum As(V) adsorption capacity of 1.49 mg As(V)/g compared to 1.26 mg As(V)/g of FB. Both the adsorbents showed similar type of behavior with varying magnitude. As(V) adsorption was independent of the ionic strength suggesting an inner-sphere surface complexion mechanism. The kinetics of the As(V) adsorption could be best explained by pseudo-second-order rate equation. The adsorption was found strongly pH dependent, with maximum adsorption over a wide range of pH ∼ 4.0 to 7.5. The column study results showed that at a adsorbent bed depth of 30 cm and feed flow rate of 50 ml/h, the RB was capable of treating 256 bed volumes of As(V) contaminated water (Co = 1.79 mg/L) before breakthrough (Ce = 0.01 mg/L).