Treatment of boron, arsenic and sulphate from boric acid factory wastewaters using metal hydroxides

After boric acid production in Turkey, wastewater containing boron, sulfate, arsenic and gypsum is generated. These wastewaters are stored in impermeable dams and pose an environmental risk in the future or in various disaster periods. Therefore, these wastewaters need to be treated. In this thesis, it is aimed to treat boron, sulfate and arsenic from boric acid factory wastewater in Emet by using Ca(OH)2, Mg(OH)2 and Fe(OH)3. Boron treatment conditions were determined for these adsorbents, and then optimization was applied for boron, sulfate and arsenic using a central composite design. The amount of adsorbent, initial pH, temperature, mixing speed were chosen as experimental parameters in boron treatment for calcium hydroxide. Optimum parameters were determined as natural pH (5,32-5,68), 20 °C, 15 g/l adsorbent, 300 rpm stirring speed. The amount of adsorbent, initial pH, temperature, mixing speed were chosen as experimental parameters in boron treatment for magnesium hydroxide. Under these conditions, optimum parameters pH (10), temperature 30 °C, 20 g/l and 300 rpm were determined. The amount of adsorbent, initial pH, temperature, dilution were chosen as experimental parameters in boron treatment for iron hydroxide. Under these conditions, optimum parameters were determined as pH (8,5), 20 °C, 20 g/l and (0:0) dilution. In the optimization studies, nearly 90% boron was removed for calcium hydroxide, while 100% arsenic and approximately 40% sulfate were removed. Again, from the optimization studies, 13% boron was removed for magnesium hydroxide and 100% arsenic was removed. %80 boron and 100% arsenic and sulfate were removed from the iron hydroxide optimization studies. The kinetic analysis for calcium hydroxide and iron hydroxide showed that the second-order model was suitable, while the pseudo-second-order model was suitable for magnesium hydroxide.