The radiation from Zn⁶⁵ has been investigated in a thin lens beta ray spectrometer. A spiral baffle was used to discriminate between positrons and negatrons. Gamma ray energies of 1.12 and 1.4 mev have been measured as well as annihilation radiation of .51 mev. A positron end point at .32 mev has also been measured. Fairly intense internal conversion was found. A decay scheme has been proposed in which Zn⁶⁵ decays by K-capture to a 1.4 mev excited state from which it proceeds to an Intermediary state by emission of a gamma ray. The alternative positron emission is to the intermediary stage from which both paths descend to the 65 ground state of Cu⁶⁵ with the emission of a 1.1 mev gamma ray. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The kinetics of zinc extraction from perchlorate solutions with di(2-ethylhexyl) phosphoric acid in n-heptane have been measured using the rotating diffusion cell technique. The extraction of zinc is controlled by the mass transfer of reactants (Zn²⁺ and D2EHPA) to the interface. At low zinc concentrations, the system is controlled by the aqueous transport of Zn²⁺ to the interface; at higher zinc concentrations transport of D2EHPA becomes rate controlling. For the range of D2EHPA concentrations examined, the transport of D2EHPA is rate controlling. Bulk pH has a negligible effect, except perhaps at the lowest pH values examined, where there may be a slight decrease in extraction rate. This decrease was attributed to less favourable thermodynamics at low interfacial pH values. It appears that the chemical reaction rate is fast enough that it has a negligible effect on the overall extraction rate. A basic mathematical model was developed which is adequate for predicting the extraction rate under variable conditions of zinc concentration, D2EHPA concentration, and pH. The effect of using a partially loaded organic extractant was also investigated, and the system was found to be mass transfer controlled. An extended mathematical model was developed which predicts that the speciation of organic complexed zinc changes with increasing preload, and at high loadings the direction of ZnL₂HL and ZnL₂(HL)₂ flux reverses, with these species providing extractant to the interface. At very high loadings, ZnL₂HL provides almost all the extractant to the interface. Experimental studies of the effect of temperature on the rate of zinc extraction resulted in a calculation of the activation energy which was consistent with a diffusion controlled mechanism. Finally, the effect of different filter pore sizes on extraction was examined. The extraction rate decreases significantly with a very small filter pore size, while there appeared to be little or no effect for larger filter pore sizes. For the filter pore size used in this study, it was therefore concluded that the filter pores do not pose an additional resistance to mass transfer. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The applicability of microbiological oxidation for the recovery of zinc from a high-grade zinc sulfide concentrate has been investigated using a pure strain of Thiobacillus ferrooxidans. Factors affecting the bacterial activity and consequently the rate and extent of zinc extraction were studied. These factors were: temperature, pH, nutrient and substrate concentrations, solid particle size and surface area. The effect of carbon dioxide concentration in the air supplied to the oxidation was also studied. Larger scale experiments were carried out to simulate more closely possible industrial conditions. The optimum temperature was found to be 35°C, the optimum pH 2.3. Nutrient levels of 89 mg phosphate P/l and 636 mg ammonia N/1 were sufficient to avoid rate limitation and provide for maximum extraction, respectively. Increasing the particle surface area, the pulp density, or the total surface per unit volume of leach liquor increased the rate of zinc extraction up to a point beyond which further increases were not effective. Increasing the carbon dioxide content of the air had a similar effect. The larger scale experiments gave similar extraction rates to those observed in shake flasks but the extent of zinc extraction was significantly higher. The final concentration of zinc in leach solutions reached levels currently-employed in commercial electrowinning procedures. A form of the generalized logistic equation was shown to be capable of representing the complete extraction curve under a variety of experimental conditions. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Zinc-titanium alloys (0.07-0.6 wt.%Ti.) in the form of compacted powder and chill castings have been extruded at temperatures between 150°C and 350°C. The mechanical properties of these alloys have been studied as a function of temperature, strain rate, grain size and intermetallic (Zn₁₅Ti) distribution. Due to a high value of "k" in the Hall-Petch relationship, maximum strengthening is obtained by a reduction in grain size. However because of an increasing amount of grain boundary shear, this potential is not realized. The operation of dynamic recovery mechanisms at 20°C and higher also results in limitations upon the development of high strength. The use of powder metallurgical techniques gives rise to the formation of intermetallic distributions which inhibit these processes and results in high strength (>60,000 p.s.i.) and low strain rate sensitivity (m ∼ 0.02). The mechanical properties are not a function of initial powder size. The properties obtained using chill castings do not reach these levels due to the difficulty associated with forming a fine second phase on solidification. Such a distribution is required to obtain a small stable grain size during subsequent extrusion. To satisfy compatibility requirements deformation modes other than the two supplied by basal slip must be invoked. High strengths are observed when grain boundary shear and migration are inhibited by the distribution of the second phase or by orientation effects. Under such conditions, non basal slip and basal slip are the operative deformation mechanisms. Significantly lower strengths result if grain boundary shear and basal slip satisfy the conditions necessary for ductile behaviour. The strain rate sensitivity parameter at 20°C lies in the range 0.02-0.07. Varying amounts of grain boundary shear occur, nevertheless deformation is slip controlled. Increased strain rate sensitivities are observed at high temperatures, but failure by cavitation limits ductility. The strain rate sensitivity is not a function of titanium concentration. Under constant fabrication conditions the strength generally increases with increased Zn₁₅Ti content. The thermal stability of the intermetallic distribution prescribes the fabrication conditions which must be used to develop high strength, and the temperature to which the mechanical properties can be retained. The high strength microstructures appear to be stable up to at least 150°C for short periods of time. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The spark spectra of zinc have been photographed in the region λ350 Å to λ8000 Å using a three metre normal incidence vacuum grating spectrograph, a twenty-one foot Eagle-Paschen " in-plane" grating spectrograph, and a Hilger E478 large automatic prism spectrograph with interchangeable glass or quartz optical trains. The spectra were excited using a condensed spark in helium source, a hollow cathode discharge, and a condensed electrodeless discharge source. In all, 5982 spectral lines were measured. Sixty-four line classifications were made in Zn I from previously established energy levels. Three hundred and seventy-one line classifications were made in Zn II, and 33 new levels were established. In Zn III, major revisions and extensions have led to a total of 1259 line classifications and 264 energy levels were established, 44 of which had been determined previously. Revisions to a previous report on the spectrum of Zn IV have resulted in an increase of the number of classified lines to 329. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This work was undertaken to study the nature of the deformation mechanisms in polycrystalline zinc and cadmium over a temperature range from 77°K to 300°K. It has been observed that the only non basal slip system which is observed under normal light microscopy is that of second order pyramidal [ll22] <ll23>. At temperature above [formula omitted], the amount of non basal slip is greater in zinc than in cadmium. The amount of twinning, substructure formation and grain boundary migration is comparable in both systems. Negative work hardening beyond the U.T.S. at temperatures above Tн = .4 is associated with recrystallization. In both systems at temperatures below Tн = .26 a region of temperature and strain rate independent linear work hardening occurs. The extent of linear hardening increases with decreasing temperature below Tн = .26. Above Tн = .26, polycrystalline hardening in both systems is parabolic from yield on and the rate of hardening at a given value of strain decreases with increasing temperature. Cadmium single crystals showed a similar trend in that below .26 both [formula omitted] remained constant. However above .26 there was a steady decrease in the shear hardening rates. It was observed that the Cottrell-Stokes law is obeyed only in the linear hardening regions of polycrystals and in Stage II hardening of single crystals below .26. When dynamic recovery occurs [formula omitted] increases with increasing strain. It has been observed that below .26 the linear hardening rate in cadmium decreased with increasing grain size ( constant specimen dimensions) so that [formula omitted] The value of [formula omitted] was shown to correspond to the tensile hardening rate during Stage II single crystal deformation. The tensile hardening rate was used because of the extensive twinning found to be associated with Stage II hardening. The grain size dependence of 0 has been interpreted in terms of a grain size dependence of the extent of [ll22] <1123> slip. It was found that during linear hardening in both zinc and cadmium the difference in flow stress at two different temperatures is a reversible difference implying that the dislocation configurations produced with increasing strain do not vary in nature or extent with temperature. Under such conditions it is possible to formulate a mechanical equation of state. Extensive rate theory measurements have been made in both systems in order to attempt an evaluation of the rate controlling mechanisms both during linear hardening and.during dynamic recovery. The former has tentatively been associated with intersection. Dynamic recovery on the other hand has been linked to the loop annealing observations of Price. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Zinc is an essential biological trace element required for proper immune functioning. Zinc deficient individuals have been reported to suffer compromised immune responses and increased levels of inflammatory cytokines. Inflammation is integral to the pathology of many disease states, ranging from pathogen dependent infectious disease to non-infectious disease such as cancer, heart disease, diabetes and stroke. One of the main mediators of inflammation is the pro-inflammatory cytokine interleukin-1beta (IL-1beta). Production of IL-1beta occurs via a two step process; firstly the transcription of an inactive pro-form is initiated, followed by protease activation leading to the cleavage of IL-1beta to a mature form. Here it is shown that in vitro zinc depletion of macrophages, using the zinc chelators TPEN and DTPA, leads to pro-IL-1beta cleavage and furthermore to increased release of active IL-1beta. This would suggest that zinc depletion induces activation of proteases that cleave IL-1beta. Caspase-1, ASC, PP2A, cathepsin B and cathepsin G are all shown to regulate zinc depletion-induced IL-1beta release in macrophages. The cell death proteins XIAP and caspase-8 have also been identified to be regulated by zinc depletion in macrophages and there is literature to suggest that these proteins may contribute to IL-1beta processing and release. By identifying a role for zinc depletion in IL-1beta processing we move closer to identifying potential therapeutic targets for zinc deficiency induced inflammatory disease. Zinc also has regulatory roles in the expression of IL-1beta. Here a systems biology approach is utilised to create an explicit representation of the pathways involved in IL-1beta expression. In many in vivo and in vitro models, transcription of pro-Interleukin-1beta is induced by the gram negative cell wall component lipopolysaccharide (LPS). A systematically curated network map of IL-1 transcription has been created. The map encompasses interactions at the macrophage cell membrane, where LPS binds Toll-like receptor 4 (TLR4); the resulting cytoplasmic signalling cascades, including MAPK and NF-kappaB; and finally the specific transcription factor interactions in the nucleus. By creating this model we aim to enable the production of dynamic models of IL-1 transcription.

Dihydroorotase (4,4—dihydroorotic acid amidolyase, EC 3.5.2.3.) which catalyzes the reversible cyclization of N-carbamyl-L-aspartate to L-dihydroorotate has been purified from orotate-grown Clostridium oroticum. The enzyme is stable in 0.3 M sodium chloride and 10 µ ZnSO4. Sodium dodecyl sulfate gel electrophoresis indicates the enzyme to be composed of two identical subunits each with a molecular weight of 58,000 + 6000. Dihydroorotase is shown to be a zinc-containing metalloenzyme with 2 g atoms of zinc per 58,000 g of protein. The role of zinc in dihydroorotase is discussed.

Indiana University-Purdue University Indianapolis (IUPUI)

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the Degree of Master of Science in Engineering. / Laboratory experimentation were conducted to investigate the regeneration and recycling of nitric acid during leaching in froth (LIF) processing of Gamsberg zinc sulphide concentrate. Two experiments were performed in a mechanically stirred batch reactor at 80- 90°C to determine the leaching kinetics of the zinc sulphide concentrate. 93 to 97% of zinc was extracted into spent zinc sulphate electrolyte containing 30 to 40g/1 nitric acid during 40 to 60 minutes of leaching without regeneration of nitric acid. Between 60.72. and 97.79% of the consumed nitric acid was regenerated after 45 minutes of batch L/F experiments carried out at 80·90oC and 50kPa. The results show that the degree of nitric acid regeneration is inversely proportional to the concentration of nitric acid in the leaching solution. Zinc extraction ranged between 56.31 and 78.37% whilst 40.29 to 50.99% of the initial sulphide sulphur was oxidised to elemental sulphur. In the continuous L/F experiments conducted at 80- 90°C and 100·200kPa, the degree of nitric acid regeneration varied from 33.63 to 97.22%. Overall zinc extraction was about 62% whilst 47% of the sulphide sulphur reported as elemental sulphur after 60 minutes of processing. A five-stage L/F processing of the concentrate was carried out in which the flotation phenomenon was used for selective separation of the floatable fraction from the nonfloatable fraction. About 40 to 80% of the consumed nitric acid was regenerated, 88.94% of zinc was extracted whilst 55.65% of the sulphide sulphur reported is elemental sulphur after 77 minutes of processing. The recoveries of zinc and elemental sulphur increased to over 92% and 58% respectively when the leach residue was subsequently leached in the batch reactor. / Andrew Chakane 2019