Waste gypsum from intermediate dye industries for production of building materials

Paper presents the studies on characterization, beneficiation and utilization of H-acid gypsum, a waste material produced by the neutralization of free sulphuric acid collected during the formation of intermediate dyes. The waste gypsum contains impurity of organic matter like nitro compounds, naphthalene etc. The removal of impurities and improvement in colour was carried out by scrubbing with water, centrifuging and drying. The beneficiated H-acid gypsum was calcined to form β-hemihydrate plaster. The plaster was tested and evaluated for engineering properties such as compressive strength, bulk density, water absorption and porosity. These properties suggest the use of beneficiated H-acid gypsum for making building and ceramic grade plasters and for casting building blocks, board and cementitious binder. Data showed that cementitious binder of low water absorption (9.5%) and adequate compressive strength (19.6 MPa at 28 days) can be produced for use as construction material. The use of waste gypsum will definitely benefit environment and sustainable development.