The effect of thermal treatment on the acid neutralizing capacity of newberyite: structural assessment and kinetics of the HCl neutralization reaction

Abstract

The newberyite MgHPO4·3H2O antacid activity has never been investigated before. Crystalline and heated Newberyite, at 200 °C, was tested as a neutralizing of hydrogen chloride acid (HCl 0.1 M to simulate gastric juice). Results show that the substrate has a basic behavior and may be used as an active ingredient in the antacid formulation. HCl Neutralization 0.1 M depends of newberyite concentration and pH1 was reached when 0.5 M was used. The crystalline and heated newberyite antacid power was compared with that of some commercial antacids. The newberyite heated pushed pH to 4 after 4 min when the crystalline product was brought it to 3 after 15 min. The antacid neutralizing capacity (ANC) was evaluated using direct and reverse titration methods. ANC values increased when particle sizes decreased. The heated product at 200 °C increased strongly the ANC and the maximum value reached was 13 meq/g. The kinetic study of neutralization reaction was carried out by pHmetry. The rate constants are depending of newberyite quantity and the optimal neutralization of HCl 0.1 M was obtained for 0.5 g. The resulting structural transformations have been investigated. XRD showed that the product became amorphous after heating at 200 °C. FT-IR and Raman spectroscopy agree on departure of the three crystallization water molecules, when MgHPO4·3H2O was heated. Surface area measurement was determined by Brunauer, Emmett and Teller and indicates that the product hasn’t an important porosity. Scanning electron microscopy coupled with energy dispersive spectrometry elementary analysis was also carried out and confirmed FT-IR and Raman spectroscopy results.