C.P.J. Van Vuuren

The thermal decomposition of cerium(III) nitrate

The thermal decomposition of anhydrous Ce(NO3)3 has been studied. The thermal decomposition reaction is described by the second order kinetic equation, [1/(1−α)]−1=kt. The apparent activation energy was determined asEa=104 kJ mol−1 while the enthalpy of the reaction was estimated asδHr=111.1 kJ mol−1. The decomposition reaction differs from that observed for Nd(NO3)3.ZusammenfassungDie thermische Zersetzung von wasserfreiem Ce(NO3)3 wurde untersucht. Die thermische Zersetzung wird durch die Geschwindigkeitsgleichung zweiter Ordnung[1/(1−α)]−1=kt, beschrieben. Für die scheinbare Aktivierungsenergie wurde ein Wert von 104 kJ mol−1 und für die Enthalpie der Reaktion ein Wert von 111,1 kJ mol−1 ermittelt. Die Zersetzungsreaktion unterscheidet sich von der für Nd(NO3)3.РЕжУМЕИжУЧЕНО тЕРМИЧЕскОЕ РАжлОжЕНИЕ БЕжВОДНО гО НИтРАтА цЕРИь. РЕАкцИ ь тЕРМИЧЕскОгО РАжлОжЕНИь ОпИсыВАЕ тсь кИНЕтИЧЕскИМ УРА ВНЕНИЕМ ВтОРОгО пОРьДкА: [1/(1−А)]− 1=kt. ОпРЕДЕлЕНы кАжУЩАьсь ЁНЕРгИь Ак тИНАцИИЕa, РАВНАь 104 кД ж · МОль−1, И ЁНтАльпИь РЕ АкцИИδHr, РАВНАь 111.1 кДж · МОль−1. Р ЕАкцИь РАжлОжЕНИь От лИЧАЕтсь От НАБлУДАЕМОИ Дль НИ тРАтА НЕОДИМА.

The high temperature oxidation of FeV2O4

Abstract The high temperature oxidation of FeV2O4 was investigated by means of thermoanalytical techniques and X-ray powder diffraction. FeV2O4 is oxidized to FeVO4 and V2O5 through intermediates such as R2O3 (a solid solution of α-Fe2O3 and V2O3), VO2, V6O13 and FeV2O6. Depending on the heating rate, self-heating due to exothermic processes inhibits oxidation by the formation of a V2O5 crust.

The oxidation of FeV2O4 by oxygen in a sodium carbonate mixture

Abstract The oxidation of FeV 2 O 4 , synthetic coulsonite, in a sodium carbonate mixture was studied by using thermal analysis and X-ray powder diffraction techniques. The vanadium is converted to water-soluble sodium vanadates in the temperature range 300°C to 800°C. Product formation is dependent on the amount of sodium carbonate present in the mixture. Na 3 VO 3 and Fe 2 O 3 were formed in a stoichiometric mole ratio of FeV 2 O 4 :Na 2 CO 3 of 1:1 whereas Na 3 VO 4 , Na 4 V 2 O 7 and Fe 2 O 3 were formed in a 2:5 mole ratio mixture and Na 3 VO 4 and NaFeO 2 in a 1:5 mole ratio mixture. This temperature is much lower that the processing temperature of ∼1050°C currently used for the roasting of a titaniferous magnetite ore.

The leaching behaviour of a nickel concentrate in an oxidative sulphuric acid solution

Abstract The oxidative leaching of a nickel sulphide concentrate in sulphuric acid solution was investigated. Both NaNO 3 and Fe(III) were investigated as possible oxidizing agents. Nitrate was found to give better leaching rates than Fe(III). The reaction followed a surface controlled reaction mechanism, 1 − (1 − X ) 1 3 = kt , during the initial stages of leaching. The activation energy of the chemical reaction was calculated as 88 kJ/mol in the temperature range 60°C to 95°C. Sulphur forms as a product during leaching and tends to inhibit the leaching rate, probably due to the formation of a sulphur layer on the concentrate particles during this stages of the reaction, a diffusion controlled mechanism became operative.

The oxidation kinetics of FeV2O4 in the range 200–500°C

Abstract The oxidation kinetics of FeV2O4 were studied using isothermal and non-isothermal methods of analysis. The isothermal experimental data are described in terms of the Jander equation with Ea = 141 kJ mol−1. The non-isothermal analysis showed that the kinetics can be described in terms of three different overlapping processes. The first process, oxidation of the spinel to give a solid solution, is described in terms of a first-order nucleation mechanism, Ea = 61 kJ mol−1, and take place in the temperature range 180–380°C. The second process, the oxidation of the solid solution, takes place from ≈ 360°C and is described by a diffusion mechanism with Ea = 249 kJ mol−1. The third process, oxidation of the remaining spinel, is described by a first-order nucleation model with Ea = 345 kJ mol−1 and overlap with the second process. The reaction is completed at ≈ 580°C.

The thermal decomposition of neodymium nitrate

Abstract The thermal decomposition of Nd(NO3)3 was reinvestigated. The decomposition kinetics are described by a diffusion mechanism. The rate constant was found to be temperature dependent below 390°C with an apparent activation energy of 805 kJ mol−1 and almost temperature independent above 390°C with an apparent activation energy of 65 kJ mol−1. The enthalpy of decomposition was estimated as 208.6 kJ mol−1 Nd(NO3)3 at atmospheric pressure and decreased to 187.3 kJ mol−1 Nd(NO3)3 at high pressure.

Gold losses from cyanide solutions Part I: The influence of the silicate minerals

Abstract Shale material from Beatrix Gold Mine in South Africa has been found to be capable of adsorbing gold from cyanide solutions. Black shale bands occur in the reef zone at Beatrix Mine, but because of the mode of occurrence of the shale bands selective mining cannot be practised and ore delivered to the plant is contaminated by shale. Petrographical investigations and gold adsorption experiments were undertaken on samples of these shales, in an attempt to quantify their gold adsorption properties. Mineralogically the shales comprise muscovite, chlorite, pyrophyllite, and chloritoid which suggest that the shale is a low grade metamorphic rock. Gold adsorption experiments have shown that over time there is a drop in pH of the gold cyanide solutions. This is caused by decomposition of the phyllosilicates in the strongly alkaline solutions. Analysis of these solutions showed that high amounts of Si and Al are present. No Mg and Fe have been detected in the solutions which suggests that any dissolved Mg and Fe precipitate immediately on the surface of the solids so that gold can co-precipitate with colloidal Mg(OH) 2 and Fe(OH) 3 . It was found that a tendency exists for high gold adsorption values to be preferentially related to high percentages of FeO (corrected for pyrite) + MgO + Al 2 O 3 (corrected for muscovite) in the shales.

The thermal decomposition of lanthanum(III), praseodymium(III) and europium(III) nitrates

Abstract The thermal decomposition kinetics of some anhydrous lanthanide nitrates were investigated and compared with those of neodymium nitrate. The kinetics of the decomposition reaction of La(NO 3 ) 3 and Pr(NO 3 ) 3 are described by the contracting area and contracting volume mechanism, respectively. The enthalpy of decomposition amounts to 123.4 and 102.6 kJ mol −1 , respectively. No reversible changes were observed for these two nitrates. The decomposition reaction of Eu(NO 3 ) 3 is similar to that of Nd(NO 3 ) 3 in so far as a reversible change occurs simultaneously with the decomposition reaction, causing a change in the temperature dependence of the rate constant. The enthalpy of decomposition was estimated as 119.6 kJ mol −1 . Decreasing ionic size of the metal ions appears to decrease the thermal stability of the nitrate, as manifested by the values of the temperature of initiation of decomposition.

Computerized application of the Zsakó method of analysis

Kinetic parameters and mechanisms of solid state reactions can be determined from a single non-isothermal experiment using the Zsakó method. This method has been computerized and applied in theoretical and practical studies and in the separation of overlapping reactions.ZusammenfassungUnter Anwendung der Zsakó Methode können kinetische Parameter undMechanismen von Feststoffreaktionen aus einem einzigen nichtisothermen Experiment ermittelt werden. Diese Methode wurde computerisier und bei theoretischen und praktischen Untersuchungen sowie bei der Separierung von überlappenden Reaktionen angewendet

Thermodynamics of complex formation reactions in non-aqueous solvents: Part 2. Reaction of silver(I) with N,N,N',N'-tetramethylene diamine in acetone, methanol and ethanol

Non-aqueoas solvents such as acetone, ethanol and methanol are extensively used as media for the preparation of coordmatlon complexes Reactions of these complexes, such as hgand exchange reactions, are normally carned out m non-aqueous solvents Very little is, however, known about the thermodynarmcs of complex formation reactions m non-aqueous solvents The thermodynarmcs of the reaction between silver(I) and pyrldme as well as substituted pyndme hgands m acetone were reported recently [l] This study was continued and extended to include the effect of the solvent on the thermodynanucs of the complex formation reaction The Ag+/N, N, N ‘, N ‘tetramethylene dlamme (tmen) system was chosen as model for the mvestlgation