Phosphogypsum waste as additives to lime stabilization of bentonite

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 byproduct 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.

Development of a New Ecological Material Based on Moroccan Industrial Wastes for Road Construction

“…The addition of PG to the bentonite+8% lime mixture increases the compressive uniaxial strength. The maximum value is obtained by adding 8% of PG (Figure 3 b), which is in agreement with the results obtained by Oumnih et al [26]. Using more than 8% of PG, there is a remarkable drop in mechanical strength.…”

“…When 8% of PG is added, a peak at 3411 cm -1 appears which is attributed to the symmetrical and asymmetric stretching of the OH bond of hydrated water in the gypsum molecule CaSO4.2H2O [26].…”

“…Recently, several studies aimed at valorizing PG to improve road pavements and stabilize swelling behavior of soils have been realized [23][24][25][26][27][28]. PG was also used as aggregates for bricks masonry materials [29,30] and for the production of cement [31,32].…”

Phosphogypsum and Black Steel Slag as Additives for Ecological Bentonite-Based Materials: Microstructure and Characterization

“…The maximum value is obtained by adding 8% of PG (Figure 3B), which is in agreement with the results obtained by Oumnih and al. [30]. Using more than 8% of PG, there is a remarkable drop in mechanical strength.…”

“…Recently, several studies aimed at valorizing PG to improve road pavements and stabilize the swelling behavior of soils have been realized [27][28][29][30][31][32]. PG was also used as aggregates for bricks masonry materials [33,34] and for the production of cement [35,36].…”