Pretreatment of industrial phosphoric acid

by dolomitic sediment:

optimization using design of experiments


Y. Bounou1, D. Zakaria1*, K. Ibno Namr2

1 Laboratoire de Physico-Chimie des Matériaux (LPCM), Département de Chimie

2 UR Sciences du sol et environnement (LGMSS – URAC 45), Département de Géologie

Université Chouaïb Doukkali, Faculté des Sciences, BP20, 24000 El Jadida Maroc.

* Corresponding author: E-mail:

Received: 19 June 2012; revised version accepted: 03 October 2012



The pretreatment of phosphoric acid (54 wt% P2O5), obtained from Moroccan apatite by the wet processing route, was carried out for sulphate, fluoride and organic matter removal. Natural sediment based on dolomite and silica gave encouraging results for the removal of these impurities. For eventual valorization and uses of this material on an industrial scale, a simple protocol which can be inserted into the manufacturing process, is proposed for phosphoric acid pre-treatment. Central composite design has been used to determine the optimal operating conditions, taking into account the industrial constraints, by studying of the effects of process factors (sediment weight ratio, temperature and time reaction) on the rate of impurities removal. These effects were correlated with the mechanism impurities removal. The results predicted using surface response regression model showed high values of regression coefficients (R² sulphate = 0.99, R² fluoride = 0.97 and R²organic matter = 0.97) indicating good agreement with experimental data. Optimization of the process was carried out using desirability function by targeting the factors to desired levels for maximum removal of these impurities. The efficiencies of removal of sulphate, fluoride and organic matters were 87.69%, 74.23% and 93.41% respectively, with a global desirability of 0.92. Arsenic, copper, chromium and cadmium were also removed.


Keywords: Phosphoric acid pretreatment; Dolomite; Silica; Optimization; Experimental design DOE; Desirability.

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