Cement, Energy and Environment

Introduction Soda Sanayi AS. produces sodium carbonate (soda ash) and sodium bicarbonate by using limestone, salt, anthracite, ammonia and natural gas according to the Solvay Process in Mersin. Similar to the other chemical processes synthetic soda ash production yields some wastes. Solid wastes of the soda ash plant Distiller waste of the soda ash plant contains about 2 per cent of solids. Some of the synthetic soda ash producers in Europe discharge their distiller waste directly to the sea. There are also some plants discharging liquid waste after separating the solid particles in the settling ponds to the sea or river. Settling ponds are abandoned and replanted for daily usage when filled with solid particles. Different from other soda ash plants in Europe, Mersin Soda plant applies a washing process in order to decrease the chloride concentration of the solid waste. Mersin soda plant has a soda ash production capacity of 1 million tonne per year that causes about 500,000 tonnes of solid waste with 50-60% moisture. On dry basis, solid waste amount is about 220,000 tonnes per year. Chemical analysis of a typical solid waste of the soda plant is shown in Table-1 . X-ray fluorescence spectrometer (XRF) analysis result are given in Table-2. Table-1 Chemical analysis of a typical solid waste the soda ash plant Parameter % On Dry basis Chloride (CI) Calcium Sulphate (CaS04) Calcium Carbonate (CaC03) Calcium Hyroxide (Ca(OH)2) Magnesium Hydroxide (Mg(OH)2) R20 3 (Fe203+AI20 3) Silicon Dioxide (Si0 2) 1.1 5.2 70.2 12.5* 3.9 2.9 1.2 • Value is calculated. Amount of other calcium compounds is subtracted from result of total calcium determination. Table-2 XRF Analysis of a typical soda plant solid waste Free lime 0.55 CaO 48.80 Si02 1.85 AI20 3 0.67 Fe2~ 0.65 MgO 1.84 Na20 0.66 803 0.81 Ignition Loss 41 .70 Blaine fineness value of solid waste (specific surface area) is about 5000 cm 2 /g. Fields of usage for soda plant solid waste There is information in literature about utilization of soda ash solid waste for neutralization of acidic soil, production of binding material, Portland cement, alinite cement, concrete block, brick and road coating materials. Some of the studies are summarized below. • Asim Yeginobali investigated suitability of using solid waste of the soda ash plant instead of lime in the production of plaster and masonry mortar and sandlime bricks. He published his findings as an article in 1990. He used solid waste of the Mersin Soda plant in his experiments. (Chloride concentration of the solid wastes was high since washing system was not available at that time.) • As a result of that study it was found that solid waste had hydraulic properties and could be used in the production of plaster and masonry mortar and sandlime bricks having reduced strengths. It was stated that potential utilization areas of soda waste would increase if the 62