Study On Leaching Process Of Boron Ores By The CO₂-soda Method

Element boron does not exist as a simple substance in nature.90% of boron in industrial application mainly comes from three minerals:tincal,ulexite and colemanite. Wengquangou boron minerals in Fengcheng city is the biggest lugwigite-bearing ore deposit in our country. Exploring and making use of the ludwigite-bearing ores become the current topic of boron industry because the ascharite minerals wile be used up. However, the main problem that we should take into account is to raise the activity, the leaching ratio and yield of lugwigite-bearing ores as raw materials for the production of boron componds.Recently ludwigite-bearing ores were employed as raw materials to produce borax by the CO2-soda method in a few factories, however the yield of borax is very low. In this paper, the reactions of ludwigite-bearing ores with NaHCO3, NaHCO3+Na2CO3 or CO2+Na2CO3 were investigated, respectively. The influence of NaHCO3 addition on this leaching process was investigated and the highest leaching ratio of 78% for B2O3 was found when adding 40gNaHCO3/100g minerals. With increasing the addition of Na2CO3+NaHCO3, the leaching ratio and yield of B2O3 also increased; When adding 50gNaHCO3+31.6gNa2CO3/100g ores, the leaching ratio and yield of B2O3 reached 76.01%。On the other hand, the process of ludwigite-bearing ores treated by CO2+soda was also discussed. The results indicate that there is little effect of liquid solid ratio and diethanolamine addition on this process; the highest leaching ratio of 75% was obtained at 135℃for 10h when adding 12.6g Na2CO3/100g minerals. The XRD characterizations of the leaching slags in these processes demonstrate that MgCO3 was found in these slags when using NaHCO3 or CO2+soda, and Na2Mg(CO3)2 also appeared in the slags besides MgCO3 when NaHCO3 or Na2CO3 was excessive. The yield of borax by the CO2-soda method is very low mainly because a lot of boron was water-soluble in the slag. To solve this problem, we should take three measurements. First of all, raise the grade of the lugwigite-bearing ores and reduce the slag amount. Secondly, decrease the consumption of Na2CO3, reduce the generation of MgCO3 and improve the filtration of the slag. Thirdly, use elutriation or other wash method to reduce the water-soluble boron.The reaction mechanism of ascharite treated by a CO2-soda process was researched, however there was still some arguments. In this paper, the mechanism of it was also dissussed. The results indicated that the CO2 absorption rate was equivalent with the reaction rate in the most period of the process, the CO2 absorption rate was higher than the reaction rate in the later period and the gap between them became bigger and bigger as the reaction carrying out. In later period the reaction was a controlled step, however there was no control step in the whole process.