Molybdenum concentrate roasting with an addition of Ca(OH)<sub>2</sub>
The study is aimed at establishing the influence of parameters of the molybdenum concentrate oxidative roasting (temperature, Ca(OH)<sub>2 </sub>amount and the process duration) on the separation of sulphur, rhenium and molybdenum into gas phases. The object of research consisted of a sulphide molybdenum concentrate obtained from a pilot ore batch of the Yuzhno-Shameyskoye deposit having a Mo and Re content of 37 and 0.005%wt., respectively. Oxidative roasting of a granular charge consisting of a concentrate and calcium hydroxide was carried out with a continuous air supply of 10 m<sup>3</sup>/h in a RHTH 50/150/16 rotary tube furnace (Nabertherm, Germany). Chemical composition analysis of solid materials was carried out using atomic absorption and X-ray diffraction methods. In oxidative roasting of the granular charge at a temperature of 600°C, 120 min duration and a weight ratio of molybdenum concentrate and calcium hydroxide equal to 1:1, sulphur, rhenium and molybdenum were shown to remain in the cinder by 95.8 and 100%, in the form of CaSO<sub>4</sub>, Ca(ReO<sub>4</sub>)<sub>2</sub> and CaMoO<sub>4</sub>, respectively. An increase in the mass ratio of calcium hydroxide and molybdenum concentrate resulted in an increased degree of sulphur binding; conversely, an increase in temperature reduces the probability of forming non-volatile compounds based on rhenium and sulphur. The parameters of the cinder water treatment corresponding to the extraction of Re into a 83.2% solution were determined as: duration - 90 min; temperature - 90°С; ratio of solid and liquid phases - 1:4. The proposed oxidative roasting method for deriving molybdenite concentrate ensures the complete absence of rhenium and molybdenum in the gas phase, while the sulphur content remains under the maximum permissible concentrations, eliminating the need for an expensive dust and gas cleaning system. For further separation of molybdenum and rhenium, an aqueous treatment of the cinder is proposed, maximising the transfer of rhenium into a solution to allow the possibility of its subsequent isolation by the sorption method.