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.
Enhancement of Phosphate Flotation by Ultrasonic Pretreatment
Removal of carbonate impurities in sedimentary phosphate is one of the most important issues in the industry. Poor selective flotation of those ores is due to the similarity of Physico-chemical surface properties, solubility, and electrokinetic characteristics of sparingly soluble phosphate and carbonate minerals. In this study, the effect of ultrasonic irradiation as a pretreatment method on reverse flotation of low-grade sedimentary phosphate sample from Lar Mountain deposit was investigated. Ultrasonic was utilized before flotation at different ultrasound intensity. This study was performed by two flotation approaches; i) using experimental design (Plackett-Burman method with 11 variables), and ii) try and error method. Initial mineralogical studies showed that the feed sample contains 10.34%P2O5, 48.01%CaO, and 9.22%SiO2. The collected data from experimental design were analyzed by DX7.0 software to assess the influence of each parameter on flotation performance. The results indicated that ultrasound intensity, collector dosage, and dispersant dosage were the effective parameters. The results of the try and error method showed that the conditioning time was the most effective parameter in which by reducing ultrasonic preparation time the recovery was increased relative to 33.29%. Finally, the kinetic flotation tests and SEM studies were performed. The results proved surface cleaning of phosphate minerals which treated by ultrasound irradiation that led to better adsorption of chemicals which increased the recovery and grade of P2O5 for 87.88% and 14.45%, respectively. However, the application of the ultrasonic treatment reduced the flotation chemicals’ consumption which is a prominent issue for phosphate treatment.
Neutron Residual Stress Measurements on Rail Sections for Different Production Conditions
Rail sectioning with subsequent neutron diffraction experiments has been used to assess residual stresses in the rails. In this study we present the results of neutron stress measurements performed at the NIST Center for Neutron Research (NCNR) on rail sections from rails that were produced under various conditions. Specifically, these are air-cooled, air-cooled and roller-straightened, head-hardened and head-hardened and roller-straightened. More significantly, a head-hardened and roller-straightened rail was also studied after service to elucidate evolution of the service-induced residual stresses. In the latter case both a transverse-cut slice and the central region of a 0.53 m long piece were studied. Measurements on this piece are the first in which triaxial stresses have been determined for an intact rail. Neutron strain measurements with 3×3×3 mm3 spatial resolution were successfully employed for transversally cut slices to verify the difference in the stress state depending on the production process. Although examination of slices allows determination of only two-dimensional stresses in the plane of the slice, additional measurements on obliquely-cut slices, which were also carried out, and utilization of FEM gives the possibility of reconstructing the full triaxial stress distribution. Together, these approaches provide a better understanding of rail fabrication and the possibility of improving the durability and safety of rails in the future.Copyright © 2004 by ASME