Recovery of Lime, Sulfur, and Iron from Gypsum and Pyrite Wastes

Abstract

Currently, gypsum and pyrite, two major wastes generated by the coal combustion industry, have to be land-filled. The feasibility of a new approach of recovery of lime, iron, and sulfur products from these wastes is discussed in the present work. By thermal decomposition of pyrite, 42% of the sulfur is recovered and pyrrhotite is produced. A thermodynamic analysis shows that the recovery of iron and lime from pyrrhotite and gypsum in a single-stage process is not feasible. Instead, the process has to consist of two subsequent stages. The first is the reduction of pyrrhotite with carbon in the presence of lime to produce iron, calcium sulfide, and carbon monoxide, followed by reaction of calcium sulfide with gypsum to produce lime and a concentrated sulfur dioxide stream. The kinetics of the reactions involved in the two-stage process is studied using thermogravimetric analysis. The reaction rates are favorable above 950°C and depend on initial reagent concentrations. The effectiveness of magnetic separation of the Fe/CaS mixture is studied. The amount of sulfur in the magnetic fraction depends on the reaction temperature.

Carbothermic Reduction Behavior of FeS in the Presence of CaO during Microwave Irradiation

“…(2) and/ or (3), cannot initiate at temperatures lower than 645°C in the present study. Such behavior is in good agreement with the results of Marina et al 20) and Rosenqvist 24) who also reported that the iron production from a mixture of FeS, CaO, and C is thermodynamically feasible above 650 and 730°C, respectively. Therefore, the weight loss in sample heated to 645°C in 10 min is attributed to either the fully dehydration reaction, as confirmed by XRD analysis (Fig.…”

“…(4). Figure 9 shows the reduction degree of the FeS:CaO:C = 1:1:2 mixture during microwave heating of samples heated to 1 290°C and that of a mixture with a same mole ratio after conventional heating reported by Jha et al 1) and by Kutsovskaya et al 20) It was observed that the reduction degree of samples heated for 30 and 35 min is higher than 100%. Jha et al 1) reported also reduction degree over 100% and theorized that it is because of the drainage of liquid form pellet.…”

“…Furthermore, metallization of Fe is restricted by the reduction reaction owing to a higher stability of FeO than metallic iron. 2) Kutsovskaya et al 20) studied the reduction reaction in a mixture of FeS:CaO:C = 1:1.1:1.1 and showed that a reduction of 70% attains in 120 min at 950°C and that of 95% in 30 min at 1 050°C. Hara 2) reported that the rate of reduction reaction should be higher than desulfurization reaction to prevent SO 2 emission which caused by a reaction between metal oxide and mineral sulfide.…”

Bases and Basic Materials in Industrial and Environmental Chemistry: A Review of Commercial Processes

“…FGD gypsum can also be used in agriculture 113 and can be treated to produce useful materials 114 such as lime, sulfur, and iron. 115 3.4. Sodium and Potassium Carbonate.…”

Energy Efficient Separation of Magnetic Alloy from the Carbothermic Reduction of Nkana Cu‐Co Concentrates

“…On the other hand, the activation energy of 215 kJ in the upper temperature regime (T ≥ 1273 K) is comparable to the activation energy of 239 ± 18 kJ, for the reaction between CaS and CaSO4 [41] and this is because, the reduction calcination of CaSO4 to CaO and SO2 occurs via equations 26 -28 [15]. The SO2 gas from equation 28 may react with the metal oxides according to equation 29.…”