Characteristic features of sulphide mineral DTA

Abstract

Differential thermal analysis and simultaneous electrical conductivity and evolved gas detection measurements were used to determine temperature intervals and in a number of cases the nature of the recorded transformations of 21 sulphides. For example, along with the thermal dissociation of covellite interaction with copper sulphide impurity is also found. The result of polymorphic pentlandite transformation (610-620 ~ is vaesite; in the incongruent melting of tennantite (710--735~ lautite and sulphur are formed. Dissociation of sulpharsenides is as follows: cobaltite (885--905 ~ yields cattierite and sulphur; gersdorffite (800--860 ~ yields niccolite and pentlandite; and arsenopyrite (670-740 ~ yields loellingite. Endothermic transformation of pyrite (550--580 ~ results in destruction of its superficial oxidized film. A thermal change typical for each type of iron monosulphide has been established. A method for the quantitative estimation of sulphides is based upon measurement of the gas evolved during interaction of the sulphide with solid oxidants.Two lines of approach have been followed in studies on the thermal behaviour of sulphides. Some researchers investigated the processes taking place when the specimens were heated in air [1-6], while others worked in inert atmospheres [7][8][9][10]. In the first case the processes studied involve oxidation of the sulphides in air, and the subsequent dissociation of the products formed. On the other hand, studies of the thermal behaviour of sulphides under conditions excluding their oxidation allow investigation of transformations that are free from the superposition of additional processes.Several authors, e.g. [4,7,8], point out the feasibility of utilizing DTA results for the identification of sulphide minerals. However, data in the literature on the temperature ranges of sulphide oxidation in air are largely inconsistent, and demonstrate the poor reproducibility of the DTA results. This latter finding might be explained by the large number of not readily stabilizable factors that have an effect on the thermal analytical characteristics when sulphides are heated in oxidizing atmospheres. Hence, it appears difficult to solve the problem of thermoanalytical identification in this way. It is obvious that satisfactory reproducibility of thermal analytical data is a basic condition for their successful utilization in the identification of minerals. From this aspect, information on the thermal behaviour of sulphides in inert media appears more useful (in addition, such information is also very interesting from a theoretical viewpoint).

Novel multiple methods and results in thermal analysis

“…DTA-EC-EGA (evolved gas analysis) has been used by Soviet authors for the analysis of 21 sulphide-containing compounds [14].…”

Study of the Reaction Mechanisms during the Thermal Decomposition of Arsenic Sulfide (V) at High Temperatures under Non-Isothermal Conditions

“…The mechanisms responsible for such changes are not yet entirely understood, which makes it difficult to interpret the available data [4]. Furthermore, due to the vast amount of information in this regard, the data present in the literature on sulfide reaction mechanisms and kinetics show low reproducibility and great inconsistency [5], causing the tabulated values to vary depending on the source from which they are obtained [6,7]. The arsenic's physicochemical characteristics make it difficult to study its sulfides; this causes the tabulated thermodynamic values to vary between databases.…”