Phosphorites arsenic

Phosphorites are sedimentary rocks that contain at least 15-20 wt % P2O5 (Boggs, 1995), 266. The phosphate in phosphorites primarily occurs as apatite (Ca5(P04)3(F,Cl,0H)). Typically, phosphorites chemically precipitate in deep, cold marine waters. Due to chemical similarities, arsenate may partially substitute for phosphate and the arsenic concentrations of phosphorites may exceed 100 mg kg-1 ((Matschullat, 2000), 299 Table 3.23). However, arsenic concentrations in some phosphorites (e.g. southeast Jordan) are relatively low (7-9 mg kg-1) and the arsenic is mostly associated with clay and carbonate minerals rather than phosphates (Al-Hwaiti, Matheis and Saffarini, 2005). 

Baioumy, H.M. (2005) Preliminary data on cadmium and arsenic geochemistry for some phosphorites in Egypt. Journal of African Earth Sciences, 41(3), 266-74. 

McConnell, D., 1970a. Arsenic in phosphorite and apatite. Econ. Geol., 65 64—65. 

Commercially available phosphoric acid is usually manufactured by one of two processes (Van Wazer, 1953). (i) The most cost-effective method consists of treating phosphorite with sulfuric acid, (ii) The other process involves the reduction of phosphorite to elementary phosphorus in an electric furnace or blast furnace. This consists of burning phosphorite in the presence of air in order to obtain phosphorus pentoxide, hydrating the oxide to produce up to 75%-85% phosphoric acid, and purifying the resulting product with hydrogen sulfide to eliminate arsenic. 

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