Abstract
This work deals with phosphate ions removal in aqueous solution by adsorption carried out using two clays, both in activated form. One, non-swelling clay, rich in kaolinite, is associated with illite and quartz. The other, swelling, richer in montmorillonite, is associated with kaolinite, illite and quartz. Seven factors including these two clays were taken into account in a series of experimental designs in order to model and optimize the acidic activation process favoring a better phosphate removal. In addition to the choice of clay nature, the study was also interested in the identification of the mineral acid, between hydrochloric acid and sulfuric acid, which would promote this acidic activation. Response Surface Methodology (RSM) was used for this purpose by sequentially applying Plackett and Burman Design and Full Factorial Design (FD) for screening. Then, a central composite design (CCD) was used for modeling the activation process. A mathematical surface model has been successfully established. Thus, the best acidic activation conditions were obtained by activating the montmorillonite clay with a 2N sulfuric acid solution, in an acid/clay mass ratio of 7.5 at 100°C for 16H. The phosphate removal maximum rate obtained was estimated at 89.32% ± 0.86%.
Highlights
Phosphorus is after nitrogen the fertilizing element that most often limits the development of crops [1]
The best acidic activation conditions were obtained by activating the montmorillonite clay with a 2N sulfuric acid solution, in an acid/clay mass ratio of 7.5 at 100 ̊C for 16H
The analysis of the coefficients suggests that the acid solution normality (X3), the duration of activation (X4) and clay’s nature (X7) are the most influential factors. This result would support the idea that the acidic activation would depend on the nature of the clay [40], and that montmorillonite-rich clays would be more prone to acidic activation than those, richer in kaolinite [41]
Summary
Phosphorus is after nitrogen the fertilizing element that most often limits the development of crops [1]. For this reason, to improve crop yields, fertilization with soil is recommended [2]. Phosphorus is used for the manufacture of livestock feed as well as for the manufacture of detergents. Phosphorus is absorbed by plants in soil solution and in water as monovalent ( H PO − 4 ). Divalent orthophosphate ( HPO24− ) anions, each accounting for 50 percent of total phosphorus at neutral pH (pH 6 - 7). At pH 4 - 6, HPO24− represents about 100 percent of the total phosphorus in solution.
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