Recycling of Ornamental Stones Hazardous Wastes

Abstract

Sawing and polishing of the ornamental stones always generate large amount of solid and wet hazardous wastes, which pollute the environment. In Shak Al-Thoaban area, East Cairo, Egypt, huge amounts of these wastes were accumulated, during the last years, as rejects “Solid” and wet “Sahala” wastes, representing one of the main sources of environmental pollution. The aim of this work is to characterize and evaluate these wastes for recycling in quicklime production. Hence, samples of both wastes were investigated for their chemical and mineral composition applying XRF, XRD, DTA and TGA methods. Free lime content and reactivity (RDIN) of both samples were also determined after calcination for differnt soaking times (0.25 - 2.0 hrs) at 1000℃. The results were interpreted in relation to composition and microstructure of the fired samples as revealed by TLM and SEM methods. The RDIN reactivity of the resulted lime is changeable along soaking time at 1000℃because of the microfabric of its crystallites. The lime of the “Solid” sample is preserving the original limestone microstructure that contributes in its higher RDIN reactivity values at all soaking times. The relatively higher degree of grain growth of lime crystallites in the “Sahala” sample leads to its lower reactivity. The optimum soaking times for the highest lime reactivity are 0.25 and 1 hr. for the “Solid” and “Sahala” samples, respectively. On increasing soaking time up to 2 hrs, both samples show minimum RDIN values. The “Solid” sample also gives higher free lime content than the “Sahala” one at all soaking times. It is gradually increased in the former sample up to a maximum (96% - 97%) on increasing soaking time up to 1-2hrs. On the other side, a maximum free lime (~95%) is detected in “Sahala” sample at 0.25hr soaking time and gradually decreased to (87%) up to 2hrs.