Modeling and Optimization of Two Clays Acidic Activation for Phosphate Ions Removal in Aqueous Solution by Response Surface Methodology

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%.

Modelling and Optimization of Simultaneous Removal of Ions (H2PO4-, NO3- and Cd2+) by Adsorption on Clay in Aqueous Solution by Using Response Surface Methodology

“…As we can notice, the sums of squares due to the residues are all inferior to one third due to regression [16]. The determination of coefficients are done in accordance with the required limits with R 2 0.80 et RA 2 > 0.77 [32,33] These significant statistical data permit to conclude that there is an adequacy to the degree 2 model for the follow-up of this competitive adsorption [18,16,6].…”

“…With k = 2 factors of study, 2 k tests in Full Factorial Design (FD), with 2 levels (-1 and + 1) in coded value ; 2× 𝑘 tests in star with 2 other levels in (-𝛼 et +𝛼) ; with 𝛼 = 2 k/4 . Some tests, i.e 5, was conducted in the center of the experimental domain to ensure to the final matrix a pseudo-orthogonality and an isovariance of the measures on all the domain [6,16,25]. of the center with α = 2 2/4 = 2 1/2 .…”

“…The sample was taken from a depth comprised between 2 and 2.5 m. The clay was used under its activated from 2 µm fraction ; this fraction was obtained in accordance with the protocol of Thiry et al [20] from 50 µm fraction. The protocol of activation has been described in a previous study [6]. The characteristics of this activated clay composed predominantly by smectite and kaolinite, are presented in Table 1.…”

“…This alternative needs to be easy to implement and less expensive. For this reason, clays are mostly used because of their abundance, adsorbent properties, and exchange capacities [5,6]. Discharge standards, phosphorus, and nitrate consumption are respectively set at 15 and 50 mg.L -1 in Côte d'Ivoire [7].…”