Determination of growth rate of boric acid crystals in the presence of calcium propionate

Turkey has the largest borate reserves in the world. So, it becomes more important to produce boron and its derivatives. Boric acid is a naturally accuring compound containing the elements boron, oxygen and hydrogen. It is one of the most commonly produced borates in our country but there are some problems during the crystallization. The most important problems are dentritic growth and decreasing the mean particle size with secondary nucleation, crystal agglomeration, caking tendency and high level of impurities. The problems above, the easiest one to solve is decreasing the impurities. Boric acid is produced in Turkey and Europe mainly by the reaction of colemanite with sulfuric acid leading to crystallization of gypsum. The most important problem in boric acid production from colemanite ores with H2SO4 is the formation of MgSO4 coming from the gang mineral (magnesium borate and clay minerals). The amount of MgSO4 is balanced by the discharge of the solution from the process and this leads to decrease the efficiency of the process. For decreasing the magnesium impurity in a current boric acid production process from colemanite ore, a new applicable process development that can be an alternative to the conventional one was investigated. It has been assumed that the accumulation of magnesium impurity in the system may have been controlled by the use of propionic acids, which does not decompose the clay minerals in the colemanite ores. It was shown that product quality and process efficiency could be increased and the environmental impact of the process could be decreased by decreasing the impurity intake of the solution in the new boric acid production process based on the reaction of colemanite ore with sulfuric acid in the presence of calcium propionate. However, it can be seen that there were not any systematical experiment work about effects of calcium propionate on the boric acid crystallization. The aim of this study is to investigate whether the presence of calcium propionate can effects growth and dissolution behaviour of boric acid crystals. Growth rates of boric acid are studied in single crystal growth cell and in a dense fluidized bed in the presence of calcium propionate. It was compared the growth rate in the presence of different calcium propionate concentration The effects of supersaturation and in the presence of different concentration of propionic acid on the boric acid crystals are evaluated from the photographs and measurements taken during the experiments of two methods. It was observed that the presence of calcium propionate was not affected the growth behaviour of boric acid crystal, significantly.