Phosphogypsum waste as additives to lime stabilization of bentonite

Meriam El Ouahabi,Kamal Elhamouti,Safae Oumnih,El Khadir Gharibi,Nathalie Fagel,Nadia Bekkouch

doi:10.1186/s42834-019-0038-z

Meriam El Ouahabi, Kamal Elhamouti + Show 4 more

Open Access

https://doi.org/10.1186/s42834-019-0038-z

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Abstract

Waste recycling with increasing the lifecycle of resource is a novel approach for enhancing circular economy. Within this context, this study aims to give a second life cycle to phosphogypsum (PG) waste, which is a by-product from phosphoric acid manufacture, as useful resources. This study evaluates the sustainability of this harmful waste, which is accumulated in large stockpiles and becomes hazardous during storage, and to stabilize bentonite-based concrete intended for road construction.The effect of raw bentonite (Ca-Na montmorillonite), PG, and lime on the properties of cementitious materials has been investigated through various tests. The properties examined include chemistry (X-ray Fluorescence Spectrometry), mineralogy (X-ray Powder Diffraction and Fourier-Transform Infrared Spectroscopy), calorimetry (Differential Thermal Analysis/Thermogravimetry) and microstructure (Scanning Electron Microscopy) of the mortar based on different mixtures of bentonite, PG and lime. The result show that lime and PG addition involves in the formation of new nanocrystalline phases and the disappearance of certain minerals as portlandite. Calcium silicate hydrate gel appeared in the mixture with 8% of lime, whereas strätlingite was neoformed in the mixture with 8% of lime and 8% of PG. These nanocrystalline phases are responsible for enhancing mechanical strength through the pozzoloanic reaction.

Highlights

Phosphogypsum (PG), produced from phosphoric acid production, consists mainly of CaSO4·2H2O and some impurities such as P2O5, F−, and organic substances
Characterization of raw materials The X-Ray Diffraction (XRD) spectrum of bentonite shows a dominance of smectite with characteristics diffraction peaks at 6.2, 19.9, 27.7 and 34.6 2θ (Fig. 1)
The effect of raw bentonite (Ca-Na montmorillonite), PG waste, and lime on the properties of cementitious materials has been investigated through various tests

Summary

Introduction

Phosphogypsum (PG), produced from phosphoric acid production, consists mainly of CaSO4·2H2O and some impurities such as P2O5, F−, and organic substances. Many phosphate fertilizer-producing countries face problems of PG waste with the high waste yield (5 kg PG generated 1 kg of phosphoric acid produced) [1]. The annual world production of PG has been estimated to be around 200–300 Mt [2]. Most of this byproduct (85%) is stored in large stockpiles without any treatment. In Morocco the annual production of PG is estimated at 20 Mt. In Morocco the annual production of PG is estimated at 20 Mt It is accumulated in large stockpiles which occupy vast land areas and discharged into the sea

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