In this research, graphene oxide was introduced as an efficient flotation reagent for the selective separation of molybdenite from chalcopyrite. The performance of graphene oxide and its adsorption mechanism on chalcopyrite were investigated by flotation tests, FTIR spectra, and XPS measurements. First, graphene oxide was synthesised, and then its performance was evaluated by SEM, XRD, and EDX. Flotation tests were carried out in a hallimond flotation cell with a volume of 300 ml. Optimum flotation values were achieved at pH = 9 by adding 250 g/t of PAX (Potassium Amyl Xanthate) as a collector and 50 g/t of A65 (Poly Propylene Glycol) as a frother. The results showed high recovery, around 80% for molybdenite, while chalcopyrite was depressed in high amounts by employing 11 kg/t of graphene oxide as a depressant. Compared to common chalcopyrite depressants such as NaHS, Na2S, and C2H3NaO2S, graphene oxide had a higher potency in depressing, which can be applied as a green-depressant in the separation of molybdenite from chalcopyrite by the flotation process. Also, the validity of the depressing effect on chalcopyrite was verified by XPS and FTIR spectra.

To produce the lime required for the Bayer process, two parallel flow regenerative shaft kilns (PFR) were used in the Iran Alumina plant located in Jajarm, North Khorasan Province, Iran. In this study, the calcination conditions of limestone were modelled in a laboratory furnace by considering three factors of limestone size, temperature and calcination time using the Box-Behnken method. The calcination model of limestone was obtained using a quadratic equation. Due to the importance of limestone dust in the performance of industrial kilns, conditions of calcification and its reactivity with water were examined at three temperature ranges of 800, 1000, and 1200°C, by two methods of titration and standard ASTM C110. The results indicated a decrease in reactivity of lime relative to the increased temperature of calcination and the lack of forming the burnt lime particles that stick together (blocking). Finally, the ratio of input limestone (kg) to fuel (m3) was reduced from 16.4 to 15.3 to increase the average temperature of the burning zone to 1000°C. Also, excess air was reduced from 40 to 20%. In this condition, the lime quality was increased by about 6% in the kilns.