Direct utilization of liquid slag from phosphorus-smelting furnace to prepare cast stone as decorative building material

Discharge of huge amount of liquid slag from phosphorus-smelting electric furnace has posed serious threat to the environment. In this study, a novel approach of directly recycling the liquid slag to prepare cast stone as decorative building material was proposed and experimentally tested. In our lab experiments, 76 wt.% water-quenched slag was re-melted at 1400 °C for 0.5 h (thus simulating liquid slag from phosphorus-smelting electric furnace), and then mixed with 18 wt.% quartz powder and 6 wt.% calcined kaolinitic clay, and subsequently melted together at 1450 °C for 1 h into modified liquid slag which was cast, heat-treated, annealed and transformed into cast stone. The optimal temperature for heat-treating cast stone ranges from 850 to 900 °C. And as-prepared samples present excellent properties of bending strength, acid resistance and alkali resistance. ESEM images show that their microstructures are composed of spherical granules with particle sizes of about 0.2–0.4 μm, which are non-crystalline as indicated by the results of XRD analysis. EDS results show that the contents of major elements in the granule are different from those in its background area. Results of TCLP test show that heavy metals from raw slag have been solidified in the cast stone. The practical feasibility of the new technology was examined further by on-site experiments, in which fresh liquid slag from phosphorus-smelting electric furnace was directly mixed with quartz and kaolinitic clay to produce cast stone. The results were quite stable and consistent with those of lab experiments, proving that the proposed approach of direct utilization of both energy and material of liquid phosphorus slag to produce cast stone as decorative building material is feasible, cost-effective and environment-friendly.