The kinetics of cadmium extraction from greenockite and hawleyite CdS-samples by Thiobacillus ferrooxidans has been investigated. The inoculated experiments resulted approximately 25 times higher yields of cadmium extraction than the sterile controls. Using a Monod-type equation [V = K V-m/(K+PD)], the maximum rate of cadmium extraction has been assessed from the pulp density (PD) experiments to be V-m = 212,77 mg l(-1) h(-1) and the constant value K = 0.234. The optimum temperature (degrees C) activation energy (E-a) and frequency factor (A) were derived from the data generated at temperatures varying from 25 to 40 degrees C, using an Arrhenius type equation [V = A exp(-E-a/RT)] to be 35 degrees C, E-a = 10,7 kJ/mol and A = 12.5, respectively The relatively low value of activation energy suggests that the bioleaching of cadmium sulfide mineral sample is diffusion controlled. In the range of 20 to 35 degrees C, the temperature coefficient was determined to be Q = 1.87. Based upon this experimental study a flowsheet is proposed for bioleaching of cadmium sulfides. However; the industrial application of this bioleaching technique requires further investigation on pilot plant level and an economic evaluation of the process.

This paper provides information on selected technologies available for remediation of metal contaminated soils and industrial effluent solutions. Because some of the industrial sites are contaminated with organics (solvents, gasolines and oils), an effort has been made to introduce the most frequently used cost-effective cleanup methods, such as "bioventing" and "composting." The microorganisms involved in these processes are capable of degrading organic soil contaminants to environmentally harmless compounds: water and carbon dioxide. Heavy metals and radionuclides contaminated mining and industrial sites can be remediated by using adapted heap and dump leaching technologies, which can be chemical in nature or bio-assisted, The importance of volume reduction by physical separation is discussed. A special attention is devoted to the remediation of soils by leaching (soil washing) to remove heavy metal contaminants, such as chromium, lead, nickel and cadmium. Furthermore, the applicability of biosorption technology in the remediation of heavy metals and radionuclides contaminated industrial waste waters and acidic mining effluent solutions was indicated.

Efficiency of Ca-alginate beads in the removal of Ba2+, Cd2+, UO22+ and Zn2+ from aqueous solutions was evaluated. Effects of process variables (initial metal ion and calcium alginate concentrations, pH and temperature) on the kinetics of the biosorption process were assessed. The maximum rate of metal sorption, v(m), and the corresponding diffusion coefficient, D(M2+), were derived to be:[GRAPHICS] The apparent activation energy was derived from the Arrhenius plot to be 11.3 kJ/mol. This relatively low value of activation energy suggests that the biosorption process is diffusion controlled.

In order to satisfy the high demand for gold, lower and complex grade resources must be treated in ever increasing amounts. This requires the development of new processing technologies, which are capable of recovering gold economically from these offgrade, difficult to process (refractory) ores, while safeguarding the environment. Within the novel processes, the biohydrometallurgical approach is continuously gaining importance. The microorganisms involved in these processes are numerous and the reaction mechanisms of leaching are not always understood. Some heterotrophic microorganisms may yield directly gold dissolution from the lateritic ores, while the chemolithotrophic bacteria are capable of liberating submicrometre size gold particles enclosed in the pyrite and arsenopyrite minerals. In this latter process gold remains in the bioleach residue from which it is dissolved by cyanide leaching. The present article systematically summarises the available information on bioleaching possibilities, and where appropriate, provides data on industrial applications.

Aspergillus niger, a fungus, was used in the degradation of commercially available thermoplastic polyethylene films. Quantitative calorimetric measurements performed on as-received, abiotic, and biotic treated polyethylene samples, revealed that the amorphocity of the sample decreases during biodegradation. In addition, it was found that the external substrates (sucrose) in the growth medium influenced the biodegradation process of polyethylene. Furthermore, the crystallinity data on different biotreated samples indicated that the adapted microorganisms were able to metabolize a small portion of polyethylene. The significance of the Fourier transform infrared (FTIR) results of polyethylene samples have been discussed.

The present study provides preliminary data on the involvement of such microorganisms asAspergillus niger in the biodegradation of commercially available polyethylene packaging thin films and T.ferroxodans andT. thiooxidans in pure and mixed cultures in the desulfurization of rubber samples. Further studies are in progress, and it is expected that the generated results will contribute to the solution of certain problems associated with the disposal and management of polymeric waste materials.

The apparent activation and deactivation energies and the corresponding frequency factors of coal desulfurization byThiobacillus ferrooxidans have been determined to be ΔE a = 60.9 kJ,A a = 1.45 s-1 and ΔEd = 178.3 kJ,A d = 5.65×1027 s-1, respectively. The thermo-dynamic values (AG‡, ΔH ‡, and ΔS‡) of the activated complex were calculated. Kinetic parameters of the Monod equation were determined to beV m = 55.9 mg dm-3 h-1 andK = 24.1% pulp density. The maximum rate of desulfurization of coal was found to beV m = 55.7 mg dm-3 h-1 for the particle size. The generalized second order regression equation relating the yield of desulfurization to the leaching parameters was shown to adequately predict coal extraction data and optimum values of process variables. Tank leaching studies using optimum conditions resulted coal desulfurization about 90%. The iron hydrolysis reactions involving the formation of mono- and poly-nuclear, hydroxo- and sulfato complexes of amorphous and crystalline precipitates were discussed.

The present article provides information on the application of biotechnology in the valorization of mineral resources. Biohydrometallurgy is relatively a recent development but already employed in the copper, uranium and in a limited extent in precious metal processing industries. The basic principles of bioleaching and the mechanisms of bacterial action are discussed and specific examples are given for the biohydrometallurgy of the elements. An extended treatment of microbial activity is given with regard to gold and silver recoveries from ores and leach solutions, as well as for the desulfurization of coal, to represent tendencies of most active research areas. The article discusses also the biosorption processes and gives a short review of efforts devoted to biogenetic engineering of leaching organisms.

The kinetics and practical aspects of the applicability of a new uranium leaching method — the HSS (H2O2Na2SO4H2SO4) system — in the extraction of uranium from a typical New Mexico ore was investigated in the temperature range 30–80°C and at constant pH of 4.0–6.0 ± 0.1. The effect of Na2SO4 and H2O2 concentrations, pH, temperature and Fe2+ addition on the rate and degree of uranium extraction was quantitatively established. Based on the nature of rate dependence on the H2O2 and Na2SO4 concentrations, an oxidation reaction mechanism involving sulfated Fe3+ species and H2O2, including its decomposition products (O2 and HO0 radicals) has been suggested to account for the dissolution of tetravalent uranium compounds.

The physiological responses of Thiobacillus ferrooxidans, Thiobacillus thiooxidans, and the facultatively thermophilic microbe TH3 to simulated deep solution mining conditions (elevated hydrostatic pressures and oxygen tensions) have been studied. Maximum hydrostatic pressures permitting growth of T. ferrooxidans and TH3 on ferrous sulfate were 30.4 and 25.3 MPa, respectively. Simple hydraulic compression of washed cell suspensions for 48 h at pressures ranging from 0.1 to 68.9 MPa did not affect ferrous iron oxidation upon decompression but did result in measurable impairment of sulfur oxidation by T. thiooxidans. The presence of divalent copper (5000 ppM) or hexavalent uranium (1000 ppM) in pressurized T. ferrooxidans and TH3 suspensions did not affect barotolerance as decompressed cells oxidized iron as effectively as the metal-free controls. Hydrostatic pressuress over the range 0.1 to 68.9 MPa retarded carbon dioxide fixation rates in T. ferrooxidans. Although low absolute pressures (0.1 to 6.9 MPa) coupled with hyperbaric oxygen tensions were strongly inhibitory to growth, sulfur oxidation, and carbon dioxide fixation; ferrous iron oxidation was less affected by hyperbaric oxygen.

Literature on the possibility of desulfurizing coal by microbiological leaching is limited. The earliest report was that of Zarubina et al. (1959) who indicated that 23 to 27

Concentrating solar collector assemblies of the substrate steel surface electroplated with a nickel coating followed by a thin black chrome solar absorber overlayer have been studied for the role and optimization of plating parameters such as; plating time, current density, plating bath temperature, chromic acid concentration, role of chromonyx addition agent, anode-to-cathode ratio of the plating arrangement, current efficiency of electroplating, and role of substrate finish; and over-growths were evaluated in each case for solar absorptance values. Within the range studied (3–36 min), 18 min of plating time is seen to give the highest absorptance value (96%). Current density variation, within the limits of this study (21.6–54 A/dm2) shows that an optimum absorptance (93.2%) is attained with a current density of 43.2 A/dm2. Variations in bath temperature of plating (0–30°C) yields a maximum in absorptance (93.2%) in coatings done at 10°C. The optimum value in solar absorptance (97.9%) is obtained at 375.95 g chromic acid/l (50 oz/gal) addition to the plating bath, within the range, 225.57–413.54 g/l (30–55 oz/gal), studied. Chromonyx addition agent, suggested for the plating bath, is seen to optimize at 30% of the bath volume in the range (21–33% of the volume) studied. Anode-to-cathode proportions of the plating arrangement are seen to yield a maximum absorptance (98.4%) at a ratio of 2 within the ratios evaluated (1–6 anode/cathode ratios). Current efficiencies of plating show a much higher value (92%) for nickel electroplating than for black-chrome coating (0.20%) for platings done at 10°C, 43.2 A/dm2, and an electrode spacing of 1.27 cm. Finally, the role of substrate-surface finish, evaluated through coating black-chrome onto steel and nickel or nickel sheets show absorptance values to be quite similar in both cases, (93.0%) for black-chrome on steel plus nickel arrangement and (93.1%) for black chrome plated onto nickel sheets, at 10°C for a period of 3 min, and were extremely close in value for all bath temperatures (0–30°C) evaluated. Scanning electron microscopy and replication electron transmission microscopy done on plated and plated and ion-milled surfaces of solar collector growths did not yield conclusive data, but high magnification studies of the surfaces with the scanning electron microscope indicate an alteration of growth characteristics with variations in deposition temperatures. Finally, the strength of adhesion of the plated layers onto substrate surfaces was measured through tensile testing at ambient temperature. Values attained for adhesion strength (in excess of 100 kg/cm2 in each case) indicate that the electroplated nickel and black-chrome layers are well attached to their respective substrates and possible failure of these coatings is unlikely to be due to insufficient adhesion.

Nucleation and growth characteristics of electrodeposited zinc and anodically produced zinc oxide overgrowths on atomically smooth steel field emission end forms were investigated through field ion microscopy (FIM) and scanning electron microscopy. The zinc oxide overlayers attained in an alkaline bath through the application of an a.c. were seen to be more compact and they required less time to be produced in the desired consistency than those obtained with a d.c., with identical plating parameters. The a.c. coatings were seen to be amenable to FIM analysis, thus indicating good attachment properties to substrate steel tips. Controlled field evaporation sequences through the overgrowths showed the existence of a three-layer arrangement with the initial growth next to the substrate surface changing into the polycrystalline form of the plated material through an intermediate zone of excessive defect structure. These results are consistent with earlier studies on electrodeposited nickel on steel, Cr2O3 on nickel and copper on tungsten systems for comparable depths of plated overlayers.

The present study is the investigation of the kinetics of uranium extraction from a low-grade ore using a mixed Na2CO3-NaHCO3 leachant at various air pressures from one to 68 atmospheres and temperatures ranging from 29 to 70°C. The yield and rate of uranium extraction were found to increase as a function of temperature and pressure. The highest uranium extraction was 61% at atmospheric pressure and 96.9% at ten atmospheres both after 4 h of leaching at 70°C. The activation energy was determined to be 3.86 and 3.45 kcal mole−1 at one and 10 atmospheres, respectively. The order of uranium extraction was determined to be 0.31 with respect to the oxygen partial pressure. The surface characteristics of the low-grade uranium ore and the leach residues have been characterized by scanning electron microscopic techniques.