Mechanism Investigation And Process Optimization On Activated Calcinating And Pressure Carbonization Of Boron Concentrate

As important chemical raw material, Boron compounds are widely used in the fields of metallurgical process, building materials manufacturing, agricultural production, textile processing, national defense and so on. When it comes to the boron resource of China, the raw materials of processing boron compounds are mainly szaibelyite and ludwigite.However, the long-term exploitation leads to the lack of szaibelyite resource with high boron content, and ludwigite with relatively lower grade becomes the main raw material for producing boron products. Reasonable exploitation and utilization of low-grade ludwigite is of great significance to solve the problem of boron resource shortage in China and to promote the development of boron industry.In order to solve the problems of the low boron yield in the existing boron production process, the unclear mechanism of activation and roasting of boron concentrate, and the harsh conditions of leaching solution carbonization process, in this thesis, the boron concentrate which underwent the process of magnetic and gravity separation from ludwigite as the research object, the mechanism and process optimization of activated calcinating of boron concentrate and pressure carbonization of leaching liquor were investigated systematically. The main innovative developments in this thesis are as follows:1.the effects of calcination conditions, such as temperature, time and roasting atmosphere on the reaction activity of boron concentrates obtained from magnetic and gravity separation were studied in this thesis. The reaction activity of boron iron concentrate can be improved by adjusting the calcination temperature and time, and using additives, but slightly affected by calcination atmosphere. When calcinated. in air atmosphere for 2h with CaCO3 added under following conditions of calcination temperature being 670 ?~700? and particle size being about 69.1 ?m for d0.5, the reaction activity boron concentrate could reach to 85.00%.2.the physical and chemical changes of boron-containing and non-boron-containing components in boron concentrate calcination were studied by TG-DSC, XRD, SEM, EDS.The results showed that the noron-containing components of boron concentrates mainly existed in the form of szaibelyite and ludwigite, the crystal structure of ore is complex, and szaibelyite and ludwigite are closely related. During the calcination process, the magnetite was oxidized, and szaibelyite was dehydrated and decomposed to suanite which was easily leached. The serpentine was decomposed to forsterite and dolomite was decomposed to oxides. These phase transformation made the ore particles become loose, therefore the specific surface area of the boron concentrate was remarkably increased. Furthermore, the reaction activity of the boron concentrate was improved.3.the calcinated boron concentrate was subjected to carbon leaching, the effects of calcination conditions, such as temperature, time and liquid-solid ratio, on the reactivity of boron-iron concentrate were systematically investigated. The results showed that the type of sodium salt addition had no effect on the leaching rate of the reaction. The addition of sodium salt, reaction temperature and liquid - solid ratio had slight effect on the carbonization reaction, and CO2 was the dominant factor of carbonization reaction. When carbonizated under the following conditions, the ratio of liquid to solid was 1.7: 1, the reaction time was 10h, the mass of Na2CO3 was 12.8g, the reaction temperature was 135?,the concentration of CO2 was 98%, the pressure was 0.8MPa, adding activated carbon, the leaching rate reached a peak value of 85.82%.4.The mechanism of carbon leaching of boron concentrate was studied, and the results showed that during the process of carbon leaching, only the suanite reaction was found in the boron concentrate, and the other components were not involved in the reaction. When leaching in the high-temperature and high-pressure Na2CO3 solution with CO2 passed into,suanite could be hydrolyzed, and boron entered into the solution phase and reacted with Na+ to form borax. And Mg reacted with CO3 2- to form MgCO3 and 4MgCO3·Mg(OH)2·4H2O entering into the residue phase, achieving the purpose. ofseparating boron and magnesium. Boron magnesium purpose. The key factor in the carbonization process was the reaction rate of CO2.