Beneficiation of Low-Grade Phosphate Deposits by a Combination of Calcination and Shaking Tables: Southwest Iran
Three quarters of the world’s phosphate deposits are of sedimentary origin and 75%–80% of those include carbonate gangue. In this study, carbonate sedimentary phosphate deposits of the Lar Mountains of southwest Iran are studied. These deposits consist mainly of calcite, fluorapatite, quartz, kaolinite and illite, with an average P2O5 grade of 9%–10% (low-grade). Various pre-processing and processing methods have been developed for concentrating low-grade phosphate up to marketable grade and this study aims to select the optimal method to produce an economically viable grade of phosphate concentrate from low-grade ore. Different concentration methods, including calcination and gravity separation, were applied on samples at both a laboratory and semi-industrial scale (pilot scale). Using an integrated method of calcination (performed in a rotary kiln) and shaking table for concentrating the low-grade phosphate ore, the results show promise at producing grades of 30.77% P2O5 with 60.7%–63.2% recovery.
Utilization of solid wastes from phosphate processing plants
Most of the existing phosphate rocks are of low grade. For the production of marketable phosphate commodity, these low grade ores need upgrading before being utilized. Large quantities of solidwaste materials, with considerable amounts of P2O5 content are generated in phosphate processing plants. In addition of being environmental hazards and a source of pollution for air, water and soil, these waste materials add to the production cost for waste removal. The positive use of mineral processing plant tailings is becoming a common practice nowadays, to avoid pollution hazards and to improve the techno-economics of the mineral processing plants. In this paper, the solid-waste of Sebaeya phosphate washing plant, Upper Egypt, was successfully used to produce a high grade phosphate concentrate, to produce aggregates for road paving and for concrete mixes, in brick manufacturing, pottery making, and direct application for improving agriculture soils.
The rate limiting step in the sulfation of natural limestones during fluidized bed coal combustion
Abstract A study was performed of the sulfation of naturally occurring limestones under conditions simulating the bubbling fluidized bed combustion of coal. Limestones with impurity contents ranging from 2–18% (by weight) were evaluated with respect to reactivity towards SO 2 at temperatures ranging from 750 to 935°C. It was found that the calcination rates of the sorbents were sufficiently slow so as to influence the ultimate sulfation capacities. For the conditions investigated, the calcination rate dominated the overall reaction rate initially, followed by the sulfation rate once a significant amount of CaO had been generated. Sorbent utilization was improved by increasing the operating temperature and/or lowering the CO 2 concentration in the reaction atmosphere. Higher sorbent utilization was observed for (relatively) impure limestones. The presence of impurities enhanced the rate of calcination and lowered the decomposition temperature of the sorbent, in addition to affecting (both catalytically and non-catalytically) the sulfation reaction. The results of this investigation suggest that the calcination rates of sorbents, as derived from laboratory experiments, can be used to determine suitability for use in fluidized bed combustion applications. The higher the calcination rate, the better is the performance of the limestone.