Praxis is working on a DOE/METC funded project to demonstrate the technical and economic feasibility of making lightweight and ultra- lightweight aggregates from slags left as solid by-products from the coal gasification process. These aggregates are produced by controlled heating of the slags to temperatures ranging between 1600 and 1900{degrees}F. Over 10 tons of expanded slag lightweight aggregates (SLA) were produced using a direct-fired rotary kiln and a fluidized bed calciner with unit weights varying between 20 and 50 lb/ft{sup 3}. The slag-based aggregates are being evaluated at the laboratory scale as substitutes for conventional lightweight aggregates in making lightweight structural concrete, roof tiles, blocks, insulating concrete, and a number of other applications. Based on the laboratory data, large-scale testing will be performed and the durability of the finished products evaluated. Conventional lightweight aggregates made from pyroprocessing expansible shales or clays are produced for $30/ton. The net production costs of SLA are in the range of $22 to $24/ton for large systems (44 t/d) and $26-$30/ton for small systems (220 t/d). Thus, the technology provides a good opportunity for economic use of gasification slags.