The selective oxidation of elements in molten matte and metals is reviewed and discussed from thermodynamic viewpoint,Ni vs S in nickel matte,Cr,V,Nb, Mn or P vs C in iron melts being taken as examples of practical application.On grounds of thermodynamical analysis,a concept of transition temperature of oxi- dation has been introduced,and methods of calculating the transition temperature with either the two-steps- or the one-step-method are presented.On the assumption that no nucleation energy is required for the formation of new phases (gas bub- bles and the condensed oxidation products),the transition temperature of oxida- tion is independent of the forms of oxygen present,be it gaseous oxygen,dissolved [O] in metal melts or FeO from the slag,and also independent of the pressure or activity of oxygen,but it depends solely upon the nature and activity (pressure) of the reactants and products taking part in the reaction.Furthermore,the transi- tion temperature of oxidation is not a fixed temperature,it varies continuously with the composition of the bath as the oxidation process goes on.Reducing the pressure of the gaseous product would help to lower the transition temperature of oxidation. With the transition temperature of oxidation theoretically calculated,it is possible to deduce the optimal conditions for allowing one element preferentially oxidized while leaving the other element practically intact in the bath.Small- scale experiments and industrial practices show that the concept of the transition temperature of oxidation does successfully serve as a guide to control the blowing (smelting) operation,with the result that the desired element could be oxidized selectively.The kinetic factors which influence the sequence of oxidation of ele- ments in the bath are also briefly discussed. For the desulphurization of nickel matte,the decarburization in the 18-9 stainless steel manufacture (including the AOD process)and the decarburization of high-carbon ferromanganese,the blowing operation should be run so that the temperature of the bath should always be higher than the transition temperature of oxidation corresponding with the composition of the bath.But for the dechro- mizing of pig iron,and the extraction of V or Nb from the pig iron,smelting operation should be carried on,so that the temperature of the bath should be kept always lower than the transition temperature of oxidation for the respective com- position of the bath.As regards the sequence of oxidation of P with respect to C,besides the effect of the transition temperature of oxidation,the basicity and the FeO-content of the slag for holding P_2O_5 as well as the pressure exposed to or sustained by the CO-bubbles should be both considered.

A modified Gibbs-Duhem equation has been derived with a view to evalu- ating activities of both components of a binary system from the measured ratios of the activities of the two components.This equation has been applied to a num- ber of melts of systems PbCl_2-SnCl_2,PbCl_2-CdCl_2,AgCl-CuCl,Cu_2S-FeS,PbO-BiO_(1.5), PbO-SbO_(1.5),CaO-CaF_2 and CaO-SiO_2-CaF_2 on the basis of our own experimental data as well as those reported in the literature. The method of evaluating activities of Ag and Pb from the binary phase diagram developed a long time ago has been extended to binary systems having a single AB compound.Activities in the In-Sb and Sn-Te systems have been eval- uated in this way. The use of a properly chosen non-ferrous metal instead of Fe as the solvent in the study of slag-metal equilibria with a view to evaluating activities in some ferrous slags has been shown to help in overcoming certain experimental difficul- ties.The systems CaO-SiO_2,CaO-Al_2O_3 and CaO-SiO_2-Al_2O_3 have been investiga- ted by bringing Sn or Cu into equilibrium with the slags.Our recent data on the CaO-SiO_2 system are believed to be sufficiently accurate for the first time to provide a basis for testing the validity of the Masson model.

Three kinds of partial simple solutions——partial ideal solution,partial regu- lar solution and partial dilute solution——were defined.Treating the iso-μ_A or iso-_A molecules A in the A_pB-A_qC pseudobinary system as medium and using the quasi-lattice model,the theory of partial simple solutions is presented to ex- plain the simple behaviour of ternary systems which was discussed by macroscopic thermodynamic method in the author's previous papers.Combining the above treat- ment with the Temkin's assumption,this theory may also be applied to the molten salt mixtures.The behaviour of the pseudobinary systems of type A_pB- A_qC may be: ΔS~(PE)=0,ΔG~(PE)=ΔH=0 for the ternary partial ideal solution;or ΔS~(PE)=0,ΔG~(PE)=ΔH=Lw_(BC)x_Bx_C for the ternary partial regular solution;or,over y<0.01 roughly speaking, ΔG~(PE)=K_(C(G))x_C (K_(C(G))=Lw_(BC)x_(B(A))≠0) for the ternary partial dilute solution;in which y=x_C/x_(C(A)), and ΔG~(PE)=-TΔS~(PE)=ΔG-RT{x_Bln[x_B/(x_B+x_C)]+x_Cln[x_C/(x_B+x_C)]},x is the mole fraction and L is Avogadro's number.The thermodynamic properties thus calculated are in agreement with the published experimental data for the systems AgCl-NaCl-RbCl,Na-Pb-Tl,Cd-Bi-Sn,Cd-Pb-Sn,Cd-Pb-Bi and C_(sat).-Fe-Ni respec- tively.This theory was extended to the systems of more than three components,

1.The kinetics of reaction between Cu_2S-Cu system melts and H_2 has been studied at 1150,1200,1250 and 1300℃ respectively.Their equations are: for S-rich single phase,u_S=0.717 exp(-(53.137)/(RT))(S%-α)~2p_(H_2)~(1/2)+const. for misc.gap,u_S=0.531 exp(-(67.259)/(RT))p_(H_2)~(1/2) For Cu-rich phase,u_S=44.6 exp(-(146.720)/(RT))p_(H_2)~(1/2)·S%+const. These desulphurization rate are mainly dependent upon the S concentration of melt except the miscible gap.At constant temperature and H_2 partial pressure,their sequence is u_(S(h))>u_(S(m))>u_(S(l)). 2.The mathematic model of desulphurization and activities of S and Cu in relationship to the structure of Cu-S phase diagram are: for S-rich single phase (α=19.81-19.61%S), (?)=A(constant) for miscible gap (b=1.2-19.8%S), (?)=0 for Cu-rich single phase,(0 References | Related Articles | Metrics

The equilibrium diagram for Fe-Mg-Ti-O_2-Cl_2 system at 1123K was construct- ed on the basis of thermodynamic calculation and then an attempt was made of the selective chlorination to yield synthetic rutile from ilmenite with high Mg content (Fe,Mg)TiO_3.The chlorination kinetics of Fe_2O_3,MgO,TiO_2 and ilmen- ite has been mainly studied using Cl_2-CO and Cl_2-C at 400—950℃.It was resulted that the chlorination process of simple oxide is under chemical reaction control,while that of ilmenite is dependent on the ash layer diffusion.It seems to be difficult to get a high selectivity of FeO,MgO to TiO_2 in the fluidized-bed chlorination of high Mg ilmenite (Fe,Mg)TiO_3 with solid carbon reductant owing to the thermodynamic and kinetic limitations.The“low temperature effect”and catalysis of FeCl_3 found in the chlorination process were also discussed.

Autoradiographs have shown that there is an obvious reaction between Ce and Nd in liquid iron and MgO,CaO crucible wall.For reaching the Ce-O, Nd-O equilibrium,a long smelting period and the adding of rare earth elements in several batches were needed to ensure the full reaction between the rare earth elements in melt and the crucible wall.The dissolved Ce or Nd content in iron was measured by means of radioactive isotopes ~(141)Ce or ~(147)Nd together with electrolysis in the organic electrolyte of samples.The oxygen activity was measured by solid electrolyte sensors made of ZrO_2(MgO) tube. Ce_2O_(3(s))=2[Ce]+3[O] △G*_(Ce_2O_3)=451150-161.68T lgK_(Ce_2O_3)=-(98611)/T+35.34 Nd_2O_3=2[Nd]+3[O] △G*_(Nd_2O_3)=375010-123.7T lgK_(Nd_2O_3)=-(81970)/T+27.04 The standard free energy of dissolution of Nd in liquid iron: Nd_(1)=[Nd]1% △G=19790-30.40T lgγ*_(Nd)=(4326.1)/T-4.154.

Metals such as Cr(Ⅵ),Mo(Ⅵ),W(Ⅵ) and V(Ⅴ) can be extracted by am- ines from nearly neutral aqueous solutions.The mechanism of extraction has found to be by solvation with molecular association through hydrogen bonds.The number of active hydrogen atoms attached to nitrogen atom of different classes of amine determine their effectiveness in extraction of metals by solvation.Primary am- ines with two hydrogen atoms attached to each nitrogen atom are the most effec- tive extractants in comparison with secondary and tertiary amines.Results obtained from metals extraction with amines by the present reported solvation mechanism are quite different from those obtained by the widely studied anion exchange mechanism. The oxo and hydroxo complexes of transition metals such as Cr,Mo,W and V in aqueous solutions form different types of isopolyanion at different solution pH.The electric charge density or specific charge of different isopolyanions can be used to predict the relative tendency of these species to be extracted by the amines through solvation mechanism.Experimental results confirm the prediction and indicate that by using amines as solvation extractant new processes can be developed for metal extraction and separation.

Based on the solution theory,the thermodynamical approaches to calculation of the component activity coefficients in organic phases,to determination of the thermodynamical equilibrium constant of metal extraction reaction and to predic- tion of the metal extraction equilibrium distribution are presented.Three neutral solvent-metal extraction systems,TBP-UO_2Cl_2,TBP-UO_2(NO_3)_2 and (C_7H_(15))_2SO-UO_2 (NO_3)_2,have been tested solely by thermodynamical method.Seven models have also been examined and compared,Among them,the Scatchard-Hildebrand and Guggenheim ones are more simple and convenient for calculating practice.These two models have tried all available to both quarternary and ternary organic phases.

The Cu-Fe-S-Cl~--H_2O system has been thermodynamically analyzed in view of the principle that every component in a solution is in equilibrium each other, and then the potential-pH diagram of the chalcopyrite-Cl~--H_2O system has been constructed.The thermodynamic analysis indicated that a CuCl stable region may be occurred in correspondence with certain contents of Cl in solution,and does not appear beyond this limits of Cl content.The possible way to yield CuCl from the Cu-Fe-S-Cl~--H_2O system has also been discussed.

The stability of a new hydroxamic acid type chelating extractant H106 and its extraction chemistry have been investigated.After 50 extraction-stripping cycles its loss is very little,and after long time aeration test in HNO_3 medium its stabil- ity is satisfactory.In H_2SO_4 solution,Ga and Ge may be perfectly separated and recovered by co-extraction and respective stripping.The extraction of group Ⅳ or Ⅴ elements in HCl with H106 was available at their own appropriate acidity. The mechanism of metal extraction by H106 and the stability constants of extracted species have also been studied.H 106 is a weak monobasic acid with superior stability and extractability.It forms internal complexing salts with metal ions under testing conditions through oxygen-oxygen coordination.The order of extractability of metal ions is in agreement with order of cumulative stability constants of metal complexes.It shows excellent selectivity in extraction under certain conditions.H106 gives very satisfactory results in recovery of Ga and Ge from H_2SO_4 leach liquor of residue of hydrometallurgical Zn refinery,and may also be used in the determination of micro-quantities of Ti as well as in many other fields.

The influence of HCl concentration on the extraction distribution coefficients was examined when chloro-complex acids of Pt(Ⅳ),Pd(Ⅳ),Ir(Ⅳ),Pt(Ⅱ),Pd (Ⅱ),Rh(Ⅲ) and Ir(Ⅲ)extracted by TBP.The comparative tests between TBP and trialkyl phosphine oxide were also made.After the visible and ultrared spectra observations of the organic phases and the investigation of effect of H_2SO_4 and HClO_4 on extraction,it is reasonable to point out that the extraction is regarded as the mechanism of hydration and solvation of hydrogen ions.Thus, derivation of its energy change expression,explanation of the sequence of MCl_6~(2-)>MCl_4~(2-)>MCl_6~(3-) resulted experimentally and principle of the“least cherge density”are accomplished.According to the approximate formula of distribution coefficient derived from reaction equilibrium equation,the reasons of the peak occurred in the distribution curves and the auxiliary or inhibitory effect of H_2SO_4 or HClO_4 on extraction respectively were discussed.

The Gibbs energies of the liquid and solid phases in the CaCl_2-SrCl_2 system have been calculated using the information available on the phase diagram.The Gibbs energy of the liquid phase in the ternary system NaCl-CaCl_2-SrCl_2 has been predicted from the binary properties by applying a modified version of Toop's method.The partial Gibbs energies and the activity coefficients were then calcula- ted by using computer.On the basis of above calculated results and the principle of phase equilibrium the NaCl-CaCl_2-SrCl_2 phase diagram have also been compu- ted using a program.All these calculations are important for the practice of sodium electrolysis and utilization of salt lake resources.The subregular solution model and the modified version of Toop's method are expected to be suitable for calculating a series of assymetric ternary molten salt systems of potential interests, such as NaCl-CaCl_2-BaCl_2,NaCl-SrCl_2-BaCl_2,NaCl-CaCl_2-MgCl_2,KCl-CaCl_2- MgCl_2,KCl-NaCl-CeCl_3 and so on.