Incorporation of gypsum waste in ceramic block production: Proposal for a minimal battery of tests to evaluate technical and environmental viability of this recycling process

Bio-Fibres as a Reinforcement of Gypsum Composites

Three series of tests performed on fibre-reinforced gypsum composites are described herein. Sheep wool fibres and hemp fibres were used as reinforcement. The aim was to evaluate the capability of these biomaterials to enhance the fracture toughness of the gypsum matrix. The mechanical properties were measured by means of flexural tests on small specimens, whereas scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction were used to analyse the microstructure and composition of the fibres and of the gypsum composites. As a result, wool fibres were shown to improve the mechanical performance of the gypsum matrix, better than hemp fibres. This is due to the high adhesion at the interface of the fibre and gypsum matrix, because the latter tends to roughen the surface of the wool and, consequently to increase the bond strength. This preliminary research carried out shows that this type of biofiber—a waste material—can be considered a promising building material in sustainable and environmentally friendly engineering.

Crystal regulation of gypsum via hydrothermal treatment with hydrogen ion for Cr(VI) extraction

Heavy metal-containing gypsum is a widespread hazardous waste. In this work, H⁺ was found to be the most essential factor of the mineralizers in hydrothermal treatment to completely (≥99.8%) extract Cr(VI) from gypsum waste to the supernatant, where the significant growth (from several μm to several hundreds of μm) and perfection of the gypsum crystals were observed. Moreover, with increasing concentration of H⁺, the crystal growth (undergoing Ostwald ripening process) was accelerated and the phase transformation temperature of gypsum was decreased from 110℃ (at 0.2 mol/L of HCl) to 100℃ (at 0.3 mol/L of HCl), which are favorable to enhance Cr(VI) extraction efficiency. Pilot experiments further certified this method to be practicable even in ton-scale. This work proposes a practicable and universal method to completely extract Cr(VI) from gypsum waste, and would also inspire the recycle of gypsum waste containing other heavy metals, such as As, Pb, Cd, and Hg.

Environmental and geotechnical suitability of recycling waste materials from plasterboard manufacturing

This paper presents the geotechnical and environmental suitability of recycling gypsum-based waste material produced from plasterboard manufacturing. Most of the current plasterboard manufacturing industries are dumping these wastes to landfills. Among the major impediments to recycling such waste are environmental concerns around using such recycled material, as well as proper and suitable places to use it. To investigate these, such a waste from an Australian plasterboard manufacturing company was collected and a series of geotechnical properties were tested to evaluate the materials' suitability for any engineering construction. It was found that the tested gypsum-based plasterboard materials are suitable to use as road subgrade, pipe bedding and pipe backfill material. To ascertain the environmental safety of using such material in regards to manual handling as well as contaminants' leaching into the surrounding environment, materials were thoroughly tested for more than a hundred different contaminants. Tests were conducted to evaluate both the contaminants' concentrations in the sample as well as the leaching behaviour of those contaminants. It was found that concentrations of the tested contaminants were either below the individual detection limit or the safe limit defined by the local regulatory authority.

Usage of air jigging for multi-component separation of construction and demolition waste

The use of air jigging for performing multi-component separation in the treatment of mixed construction and demolition waste was studied. Sorting tests were carried out with mixtures of equal bulk volume of concrete and brick in which fixed quantities of unwanted materials - gypsum, wood and paper - were added. Experimental results have demonstrated the possibility to use air jigging to carry out both the removal of low-density contaminants and the concrete concentration in only one process step. In relation to the removal of contaminants only, the overall performance of jigging process can be comparable with that of commercial air classifiers and automatic sorting systems. Also, the initial content of contaminants seems does not have a significant effect on the separation extent. These results are of particular importance for recycling plants processing as they represent an alternative to optimize the use of air jigs. Further investigation is needed in order to evaluate the practical feasibility of such method.