Why do relatively coarse calcareous phosphate particles perform better in a static-bed calciner? A.A. El-Midany a, b, ⁎, F.A.Abd El-Aleem a , T.F. Al-Fariss a a Phosphate and Mineral Processing Chair, Chemical Engineering Dept., King Saud University, Saudi Arabia b Mining, Petroleum, and Metallurgy Dept., Faculty of Engineering, Cairo University, Egypt abstract article info Article history: Received 25 July 2012 Received in revised form 12 November 2012 Accepted 18 January 2013 Available online 24 January 2013 Keywords: Calcareous phosphate Upgrading Calcination Bed permeability Sintering The calcination process is a direct and clean process for upgrading of phosphate ores with high-carbonate contents. In this study, calcination experiments of calcareous phosphate were conducted. Different size frac- tions were used to evaluate their performance while heating in a static-bed furnace at different calcination times and temperatures. The results showed that the calcined product of coarse particles gives a higher P 2 O 5 %. A phosphate concentrate with a grade as high as 34% P 2 O 5 was obtained. Although the larger particle size is higher in grade, the finer particles showed a higher conversion. This behavior was correlated to the change in bed-structure in terms of the particle porosity, surface area and bed permeability due to exposure to high temperatures. The fast fall in both particle porosity and bed permeability in the case of fine particles leads to the capturing of the generated CO 2 , as a calcination product, inside the individual particle or the en- tire bed till this gas forms an appreciable pressure gradient that finds its way through the cracks that appear only in fine particle bed. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Calcareous phosphate ores represent one of the difficult ores to be treated with the conventional physical separation methods and flotation [1,2]. Acid leaching and thermal treatment (calcination) methods appear to be good alternatives for upgrading of such ores especially in the case of dissemination of carbonate minerals into phosphate matrix [3–5]. Although, leaching techniques succeeded to remove carbonate mineral from phosphate ore, their attack to the phosphorus bearing minerals causes high P 2 O 5 losses, in addition to high acid consumption [6–8]. Hence, calcination was found to be a proper method for upgrading calcareous phosphate ores [9]. In addition, calcination is suitable for the production of light green phosphoric acid and consequently the production of pure, edible, super phosphoric acid. The high-purity phosphoric acid is used for manufacturing pure chemical reagents, food stuffs, livestock, soft drinks, and other pharmaceutical products. The main drawback of phosphate calcination is the great reduction in phosphate solubility; therefore, the calcined phosphate rocks are avoided in phosphate direct applications such as fertilizer industry [10]. Although the calcination process is an energy intensive process and has high capital cost, it has several advantages. Among these advantages the lower handling and transportation costs due to its reduced tonnages, lower sulfuric acid consumption, reducing or eliminating the foaming in subsequent chemical processing and the production of special and high-purity and high-priced products. In addition, the reactivity of the calcined product can be maintained by controlling the calcination temperature [11]. On the other hand, Al-Jalamid area, in the north of Saudi Arabia, rep- resents one of the huge calcareous phosphate deposits with a reserve estimation that exceeds 1000 million tons [12]. Therefore, in the cur- rent study, the upgrading of Al-Jalamid calcareous phosphate deposits by thermal treatment was conducted. The effect of calcination temper- ature and calcination time as well as the effect of particle size on the cal- cination process were investigated. The calcination behavior of different particle sizes was explained based on the particle porosity as well as voids between particles (bed permeability). In addition, the particle arrangement model was used to describe the noticed behavior. Calcina- tion tests as well as measurement techniques such as X-ray powder diffraction (XRD), scanning electron microscopy (SEM), porosity and surface area measurements were used to characterize and analyze the obtained results as a limitation of static-bed calciner. 2. Experimental 2.1. Materials A representative sample from Al-Jalamid calcareous phosphate rock, Saudi Arabia, was used in this study. The sample was subjected to primary and secondary crushing leading to a product of 100% — 3.36 mm. Sampling of the crushed product was conducted by coning Powder Technology 237 (2013) 180–185 ⁎ Corresponding author at: Mining, Petroleum, and Metallurgy Dept., Faculty of Engineering, Cairo University, Egypt. Tel.: +20 2 35678526; fax: +20 2 35723486. E-mail address: aelmidany@gmail.com (A.A. El-Midany). 0032-5910/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.powtec.2013.01.035 Contents lists available at SciVerse ScienceDirect Powder Technology journal homepage: www.elsevier.com/locate/powtec