Three nickel based catalysts were prepared by the impregnation method (Ni/Al2O3 and Ni/SiO2) and co-precipitation method (Ni/ZnO). The catalysts were characterized by XRD, ICP-OES, BET-surface area and pore volume, SEM, TEM, TPR, NH3-TPD and in-situ XRD reduction. The catalytic activity of the catalysts in the liquid phase hydrogenation of octanal was studied at 110 °C and 50 bar. The effect of water as a co-feed on the catalytic activity of the catalysts was also investigated. Generally, all the catalysts were crystalline materials. The Ni/Al2O3 and Ni/ZnO catalysts contained NiO species that were “hard” to reduce, whereas the Ni/SiO2 catalyst was the easiest to reduce, according to the TPR and in-situ XRD reduction studies. The total acidity (μmol NH3/gcatal.) of the catalysts decreased in the following sequence: Ni/Al2O3 > Ni/ZnO > Ni/SiO2. The Ni/SiO2 and Ni/ZnO catalysts had intermediate and strong acidic sites, respectively, while the Ni/Al2O3 catalyst had weak-intermediate and strong acidic sites. The BET-surface area and pore volume of the catalysts decreased in the following order: Ni/Al2O3 > Ni/SiO2 > Ni/ZnO. The conversion of octanal for all the catalysts was ca. 90 %. The Ni/SiO2 and Ni/ZnO catalysts had octanol selectivities of over 99 % and the Ni/Al2O3 catalyst had 95 % octanol selectivity. The alumina support was observed to catalyze the formation of heavy products (C24 acetal, dioctyl ether and 2-hexyl-1-decanol). The water present in the feed poisoned the alumina sites that were responsible for the formation of heavy products thereby, making the catalyst more selective (> 99 %) to octanol. For the Ni/SiO2 catalyst the presence of water in the feed caused the octanal conversion to decrease with time-on-stream. The deactivation of the Ni/SiO2 catalyst, when water was used as a co-feed, was caused by the mechanical failure of the catalyst and also by the leaching of nickel metal during the reaction. / Thesis (M.Sc.)--University of KwaZulu-Natal, Durban, 2010.

Amidines [RNC(R')NR, I] and their complexes of the nickel group metals have been studied. Accurate mass spectrometry applied to (R'=H, R=Ph; R'=CH(_3), R=Ph; R'=Ph=R) have given detailed fragmentation patterns which form the basis for the interpretation of related amidines. Differences in skeletal fragmentation patterns were noted between formamidines and acetamidines/benzamidines, (^1)H, (^13)C and (^19)F n.m.r. and mass spectroscopy of lithioamidines indicate a bidentate symmetrically bonded amidine. The reactions of amidines [RN(X)C(R^)NR] X=H, Li) with compounds of the nickel group metals, results in a wide variety of complexes; their nature depending on the amidine substituents, the metal and the synthetic route used. Complexes with N,N'chelate, or't/20-metallated, and bridging groups were prepared and characterised together with complexes containing new N,N'chelate and bridging groups, resulting from nucleophilic attack of an amidine at a coordinated nitrile. The reactions of M(PhCN)(_2)C1(_2) (M=Pd, Pt) and anhydrous NiC1(_2) with lithioamidines result in yellow Pt(Am)(_2), where Am = RNC(R')NR, red Pd(_2)(Am)(_4) and dark green Ni(_2)(Am)(_4) complexes. The platinum complexes are monomeric for the acetamidine (R'=CH(_3)), and benzamidine (R(_6)H(_5)) ligands, though for palladium the benzamidine complexes are dimeric. The nickel complexes are dimeric for the acetamidine,and benzamidine ligands. Spectroscopic studies indicate that the amidino-groups adopt a carboxylate type mode of bonding through the two nitrogen atoms, and the structure of one of the complexes, bis, N,N'diphenylbenzamicline-platinum(II) has been characterised by X-ray crystallography. The structure showed a monomeric PtN(_4) square planar unit. N.m.r. ((^19)F and (^13)C) studies have indicated fluxionality when M=Pd, R'=C(_6)H(_5), R=C(_6)H(_4)-F-p. With K(_2)MCl(_4)(M=Pd, Pt) and NiC1(_2), N,N'diarylamidines form polymeric ortho-metallated complexes, N,N' diarylformamidines and acetamidines form six-membered rings, benzamidines five-membered. Treatment of Pt(PhCN)(_2)C1(_2) with HN(Li)(C(_6)H(_5))NH results in nucleophilic attack at the nitrile and formation of Pt[HNC(C(_6)H(_5))NC(C(_6)H(_5))NH](_2). A similar reaction occurred with Pd(PhCN)(_2)C1(_2) and HNLiC(C(_4)(_9))NH.

Platinum alumnide coatings have been produced by first plating a thin layer of platinum usinq a fused salt platinum plating technique and then pack aluminizing using powder packs containingAl, NH4 C1 and Al 2 0 3 or Ni 2A1 3 , NH4 C1 and Al 203 . The chemistry and morphology of these coatings on IN-738 superalloy both in the ascoated and in the subsequently heat treated condition have been studied. The coating morphology and chemistry are highly dependent upon the thickness of the platinum layer, pack activity and time of processing. A relatively thick platinum layer (l0 pm) produced a coating with an outer Pt2A13 layer above other narrow layers. The Pt concentration decreases towards zero as the diffusion zone is approached. A second type, usually formed with a thin (5 pm) Pt layer is characterised by a marked interaction with the substrate. An outer Pt/U 2 layer is followed by a layer of NiAl containing fine precipitates of a chromiumtungsten rich phase. A lamella-like layer hiqh in chromium and other refractory elements exists at the coating/substrate interface in most of the as-coated samples. A third type of coating has been produced by a post-platinising heat treatment process prior to aluminizing. This type of coating is characterised by an outer duplex layer of PtAl 2 and Ni/U. Heat treatment of the as-formed coating results in interdiffusion between Al , Ni and Pt to produce an overall thickening of the coating layer and a decrease in the coating Al concentration. Thus a (Pt,Ni) Al or (Ni,Pt) Al outer layer may develop after heat treating these types of coatings at 1000°C for up to 1200 hours. In addition to this Widmanstatten sigma phase plates extending into the substrate are normally found beneath the outer layer after several hours' of heat treatment. Diffusion paths on pseudo-ternary phase diagrams are made to represent the phase constitution of the as-formed coatings. Isothermal oxidation tests in an oxygen atmosphere between 800 - 1000°C of different Pt-Al surfaces have been studied and the result of tests showed that the incorporation of Pt into the aluminide coatings enhance the oxidation resistance (particularly at 1000°C). Furthermore, thermal cyclic oxidation tests showed a remarkable improvement in oxide adherence over the simple aluminides.

Thesis (PhDAppliedScience)--University of South Australia, 2003.

Thesis (MAppSc)--University of South Australia, 1999

Thesis (PhD) -- University of South Australia, 1998

Thesis (PhDAppliedScience)--University of South Australia, 2003.

Producing nickel and cobalt metal by high pressure acid leaching (HPAL) of nickel laterites is becoming one of Australia's largest mineral processing industries. However, the background chemical information for this process, including the fundamental physicochemical properties of acidic metal sulphate leachate solutions, is not well known. In order to improve the efficiency of current and future HPAL plants, high quality physicochemical and thermodynamic data will be necessary. This thesis reports measurements on the densities and heat capacities of nickel and cobalt sulphate solutions and their mixtures along with detailed studies of the nature of the species present and the thermodynamics of their interconversions. Densities and heat capacities of nickel and cobalt sulphate and perchlorate solutions and their ternary mixtures were measured using a vibrating tube densimeter and a flow microcalorimeter respectively. These data were used to calculate the apparent molal volumes and heat capacities of these solutions. Standard partial molal quantities were then obtained by appropriate extrapolation procedures, along with the volume and heat capacity changes of ion pair formation. A comparison has been made between experimental densities and heat capacities with those predicted by Young's rule. Good agreement was obtained except when the degree of complexation varied significantly in the mixturesThe various ion pair species in nickel and cobalt sulphate solutions, along with those of magnesium sulphate (which is a major impurity in HPAL leachates), were reinvestigated by dielectric relaxation spectroscopy. Doubly solvent separated ion pairs, solvent shared ion pairs and contact ion pairs were shown to exist simultaneously in solution and their concentrations were determined from dilute to near-saturated concentrations. Evidence for the possible existence of a triple ion, M2SO4 2+, was also obtained in highly concentrated solutions. The equilibrium constants of the stepwise reactions and the effective hydration numbers of ions and ion pairs were also calculated. The heats of complexation of nickel(II) and cobalt(II) sulphate were determined at different ionic strengths in sodium perchlorate media by titration calorimetry. These data were fitted to a specific ion interaction model to obtain the standard state values. The corresponding entropies of complexation were calculated and were found to be the major contributor to the stability of the complexes.

A fundamental study was undertaken in order to establish the mechanisms of the leaching of pre-reduced nickel laterites in ammonia-ammonium carbonate solution. Although the process has undergone various improvements since it was first introduced, the total recoveries are still relatively low, averaging at 80% for nickel and 45-50% for cobalt. The lack of sound fundamental information regarding the mechanisms and the kinetics of the dissolution of nickel and cobalt from iron-alloy grains produced by the reduction roasting of lateritic ores is seen as the main obstacle to establishing the reasons for the lack of adequate recovery and to defining alternative processing strategies which would lead to improved extraction and better process optimisation. Based on fimdamental electrochemical studies and bench scale leaching tests, as well as on-site measurements at an industrial plant where this process is applied, the work presented in the thesis introduces significant new evidence and sheds more light on the understanding of the mechanism of the dissolution process and on the reasons for the low extractions of nickel and cobalt. It has been established that the oxidative dissolution of the iron-alloy grains formed during the reduction roasting takes place primarily via a reaction involving reduction of dissolved cobalt (111) to cobalt (11), and also that the reduction of water is not a significant component of the reactions involved in the dissolution process. Open-circuit potential measurements with various metals and iron-alloys selected to model the reduced material in various solutions which simulated the leaching conditions were also conducted and revealed that passivation takes place during the leaching process. This brings to light a possible new reason for the low recoveries of nickel and cobalt which has not been previously considered. In addition, a kinetic study was conducted, in which the dissolution rates for the various metals, iron-alloys and solutions were measured as a function of time, and the results of which shed more light on the development of the process of passivation. The passivation itself is attributed to formation of iron-oxide on the surface of the dissolving iron-alloy grains, which restricts the transfer of electrons to the reduced metal and brings the oxidative leaching reaction to an end. It has been shown that the passivation can occur in two ways. On the one hand, particularly high concentration of dispersed and dissolved oxygen in the leaching reactors causes passivation by overcoming the limiting current density for the oxidation of iron to divalent iron ions and taking the potential to the region where the direct oxidation to trivalent ions becomes favourable resulting in the formation of an iron-oxide film on the surface. On the other hand, in normally aerated solutions, the passivation of the dissolving ironalloy grains occurs due to the formation of a cobalt and nickel sulphide layer, as a byproduct of the reduction of thiosulphate on the metal surface, which in turn gradually shrinks the area available for the oxidation of iron, again leading to a situation where the oxidising agents present in the solution under standard aerated conditions become sufficient to shift the mixed potential to the region where the iron-oxide forming reaction becomes favourable. The presence of thiosulphate has a decisive role in the second type of passivation. What is more, besides preventing further dissolution of the nickel and cobalt locked in the iron-alloy matrix, the loss of nickel and cobalt by precipitation in the presence of thiosulphate can further reduce the recovery of these metals. For this reason, a method was developed for the oxidation and removal of thiosulphate fkom the actual plant liquor.

Masters Research - Master of Science / The jarosite group of compounds are yellow/brown clay like substances, both naturally occurring and synthetically produced in metallurgical processes. Jarosites have the structure MFe3(SO4)2(OH)6, where M can be numerous elements or compounds, most often potassium or sodium. The term jarosite refers specifically to the potassium form of the compound, but is synonymous with the whole group of compounds, often leading to confusion. In nature, jarosites can be associated with acid mine drainage and acid sulphate soils as an intermediate product of the oxidation of pyrite and other iron/sulphur bearing minerals. In industry, jarosites are used in metallurgical processes, synthetically produced to precipitate an easily filterable form of solid iron. Jarosites have properties that make them a chemically unstable solid. Upon decomposition the jarosite group of compounds will generate sulphuric acid. A literature review found many references to jarosites, their stability, methods of conversion to iron oxides, methods to extract reusable materials and environmental concerns. Most methods of recycling were unsuccessful. Accelerated conversion of jarosites to a form of iron oxide was a successful method of mitigating the risk of future acid generation. There were numerous specific ways of completing this task. The BHP Billiton patented nickel atmospheric leach process generates natrojarosite (sodium form of the compound) as a by-product, when extracting nickel from lateritic ores. The by-product of this process was tested for stability to understand the decomposition process. Accelerated decomposition of natrojarosite was attempted using limestone and hydrated lime at 90OC. Limestone did not react with the natrojarosite. Hydrated lime caused extensive dissolution of sodium and sulphur from the solid. However XRD analysis still reported natrojarosite as the solid material, suggesting incomplete decomposition and the formation an amorphous form of iron oxide not detected by XRD. Further decomposition tests were completed using elevated temperatures and pressures in an autoclave. Natrojarosite was not detectable in the solid phase after treatment at a temperature of 212OC, converting to haematite at temperature above 150OC. The stability of natrojarosite was measured using a number of methods on two natrojarosite samples sourced from the atmospheric leach process. The methods used were batch agitation, column testing and permeability testing. The aim was to provide a holistic result for the stability of natrojarosite if stored in a waste facility. Results obtained were compared against the standard TCLP test and found to be a more accurate method for measuring the stability of natrojarosite. The tests are more time consuming than TCLP testing but showed that natrojarosite was capable of decomposing to form sulphuric acid with time. This result was not obtained from TCLP tests, which suggested the solid material was stable. It was also found that salt water stabilised natrojarosite. Decomposition occurred in 40 and 80 days respectively, for two natrojarosite samples tested in deionised water. There was no evidence of decomposition after 150 and 280 days respectively for the same two samples. The common ion theory is thought to stabilise the natrojarosite which decomposes in an equilibrium reaction. Excess ions present in solution decrease the propensity for the solid to decompose. The two natrojarosite samples tested varied in calcium concentration. Limestone and hydrated lime were added to the natrojarosite during the nickel extraction process. Gypsum is theorised to form an impermeable layer around the natrojarosite, increasing the stability of the compound. Gypsum is sourced from the neutralisation reaction between limestone or hydrated lime and the acid generated from natrojarosite decomposition.