Use of clays by-products from phosphate mines for the manufacture of sustainable lightweight aggregates

In sedimentary phosphates mining operations, clayey layers are removed as mine wastes. The main objective of this paper was to investigate the feasibility to valorize these mine wastes as Lightweight aggregates (LWAs) by mixing them with organic wastes (sawdust and coffee grounds) which act as pore-forming agents. Thermal transformations and microstructural changes during heating were investigated using X-ray diffraction, thermal analysis, scanning electron microscope and Fourier-transform infrared spectroscopy. The bulk density, compressive strength and water absorption of LWAs were also determined. Neoformed mineral phases was characterized and correlated to the LWA microstructure. The results demonstrated that original aluminosilicated minerals, dolomite and part of quartz were involved in the mineralization process and melt abundance respectively. SEM observations displayed a tangled microstructure that results from merged particles and different pores sizes. The addition of pore-forming agent to clays waste enhanced the macro-pore formation process in comparison to the reference samples. LWAs with good performances (density 0.8-0.95 g/cm3 and compressive strength similar to 77 MPa) were successfully manufactured by mixing 25 wt% of coffee grounds or sawdusts with clayey phosphate waste. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

This study investigated the feasibility of valorizing clayey mine wastes as Lightweight aggregates by mixing them with organic wastes, and analyzed the thermal transformations and microstructural changes during heating using various techniques. The results showed that the addition of pore-forming agents enhanced the macro-pore formation process in LWAs, leading to the successful manufacturing of LWAs with good performances.