Characterization and Analysis of the Carbonation Process of a Lime Mortar Obtained from Phosphogypsum Waste.

María Isabel Romero-Hermida,Luis Esquivias,José María Franco,Vicente Flores-Alés,Antonio María Borrero-López,Francisco Javier Alejandre,Alberto Santos

doi:10.3390/ijerph18126664

Abstract

This work addresses the reuse of waste products as a raw material for lime putties, which are one of the components of mortar. 1:3 Lime/sand mortars very similar to conventional construction mortars were prepared using a lime putty obtained from the treatment of phosphogypsum with sodium hydroxide. The physical, rheological and mechanical properties of this phosphogypsum-derived mortar have been studied, as well as the mineralogical composition, microstructure by scanning electron microscope (SEM) and curing process by monitoring carbonation and ultrasonic propagation velocity. Considering the negative influence of sulphates on the hardened material, the behaviour of the material after sulphates precipitation by adding barium sulphate was additionally tested. Carbonation progressed from the outside to the inside of the specimen through the porous system by Liesegang rings patterns for mortars with soluble sulphates, while the carbonation with precipitated sulphates was controlled by diffusion-precipitation. Overall, the negative influence of low-sulphate contents on the mechanical properties of mortars was verified. It must be highlighted the importance of their precipitation to obtain adequate performance.

Highlights

Publisher’s Note: MDPI stays neutralThe industrial production of phosphoric acid is carried out from the treatment of calcium phosphate rocks with sulfuric acid
The negative influence of sulphates, present in PG, on the hardening of the lime putty obtained from PG treatment as well as on the mechanical properties of the resulting mortars has been demonstrated
Once precipitated the soluble sulphates, no anomalies on the lime putty were observed in the mortar carbonation processes, which proceeds in a similar way to conventional lime mortars

Summary

Introduction

The industrial production of phosphoric acid is carried out from the treatment of calcium phosphate rocks with sulfuric acid. The chemical reaction of the industrial wet process occurs as follows [1]: with regard to jurisdictional claims in published maps and institutional affiliations. Ca3 (PO4 ) + 3H2 SO4 + 6H2 O → 2H3 PO4 + 3(CaSO4 · 2H2 O) (1). The majority of which is calcium sulphate dihydrate, i.e., gypsum (CaSO4 ·2H2 O), called phosphogypsum (PG). The amount and chemical composition of the phosphogypsum obtained depend on the quality of the phosphate rock and the industrial process being chosen. There are about 3–7 tons of phosphogypsum per ton of wet-process phosphoric acid solution [2]. Its reuse for commercial applications is limited since the PG contains relatively high concentrations of toxic substances, such as fluorides and ammonium [5], heavy metals and radionuclides [4]

Methods

Results

Conclusion