Research On Leaching Process Of Boron-rich Slag And Colemanite By Acid

Boron is a relatively scarce chemical mineral resources, boron and boron compounds have been widely used in chemical, pharmaceutical, light industry, textiles, electronics, metallurgy, building materials, national defense, aerospace and nuclear industry, agriculture and other various areas. As for boron resources in our country, szaibelyite, which has high grade and is easy to exploit, has been unable to meet the future needs of boron industry due to the long-term mining. Although ludwigite accounts for 58% of our country's boron resources, it has not be utilized very well because of its complexity. Therefore, accelerating the development and utilization of ludwigite resources has important practical significance for easing the shortage of boron resources and developing chinese boron industry.This thesis includes two parts:the research on the leaching process of boron-rich slag and the research on the process of producing boron acid by using clominate.Boron-rich slag is by-product obtained from the separation of low grade ludwigite by the selective reduction in the electric furnace or blast furnace. The B2O3 content in boron-rich slag is about 12～17%. Therefore, it can be used to produce boron acid to replace the szaibelyite. However, the acid slurry obtained from leaching boron-rich slag is difficult to filter, which directly restricts the industrial application of boron-rich slag. In this thesis, the leaching process of boron-rich slag by acid was investigated in detail, and the key factors which affects the filtration of leaching slurry were found. Firstly, the leaching slurry was treated to dehydration by heating and the treated leaching slurry can be filtered easily; the XRD and SEM characterizations of the leaching residue indicated that the major phase of it was CaSO4·2H2O and the filtration of leaching slurry mainly depended on the growth and morphology of CaSO4·2H2O crystal. Secondly, a suitable amount of filtration aid was added into leaching slurry to form large rod crystals of CaSO4·2H2O which is also helpful for enhenceing the filtration of leaching slurry. The effects of adding CaSO4·2H2O, CaCO3, Ca(OH)2 and CaO on the filtration of leaching slurry were investigated respectively. The results show that the effects of adding CaCO3, Ca(OH)2 and CaO on the filtration of leaching slurry were bigger than that of adding CaSO4·2H2O. The XRD characterizations of leaching slags indicate that CaSO4·2H2O crystal was also formed. In a word, the filtration of leaching slurry for boron-rich slag depends on the formation and the morphology of CaSO4·2H2O crystal, and the silicic acid sol in leaching slurry has little effect on the filtration of leaching slurry.The grade of Turkey colemanite is high up to 32.78%, its main phase is colemanite (2CaO·B2O3·5H2O) and MgO is only to 2.76%. Therefore, Turkey colemanite is easy to separate and purify, and can be used to produce boron acid as raw materials instead of ascharite. The suitble leaching conditions of colemanite for producing boron acid are as follows:acid consumption,125～138% of theroy consumption; reaction temperature,85～90℃; reaction time,60min; reaction liquid to solid ratio,4:1; the leaching rate, up to 98.7%; B2O3 in the residue,0.5% to 0.7%.