| Our nation is abundant of boron resource. Except of natural borax of Tibet and Qinghai, most of resource centralized in Liaoning province in the form of ascharite and ludwigite (boron-iron ore). At present, ascharite is the main raw material of production of boric acid and borax. Liaoning region’s ascharite reserves decrease day by day after many years mining. The average grade of ascharite decreases to only about10%. The Selective reduction of ludwigite in the blast furnace will result in the Separation of boron and iron. This process will finally produce the B-containing pig iron and boron-rich slag. The grade of the boron-rich slag could be relatively high (about up to12%～17%). Since the boron-rich slag is similar to the roasting ascharite, it could replace the ascharite ore to be the source of magnesium and boron. In this paper, we studied that sulfuric acid method prepared boric acid and magnesium sulfate monohydrate and carbonate-alkaline method prepared borax through leaching boron-rich slag. We can recover boron oxide and magnesium oxide from boron-rich slag effectively.In the past, the recovery of magnesium sulfate is low in the research of preparation boric acid. It caused resource waste and seriously environmental pollution. In the crystallization experiment of boric acid and magnesium sulfate system, sulfuric acid and magnesium sulfate system and magnesium sulfate and boric acid system, we found the addition of boric acid and sulfuric acid changed the properties of magnesium sulfate solution, such as reduced the super saturation and promoted crystallization of magnesium sulfate monohydrate. While the magnesium sulfate added may be adsorbed on the surface of boric acid crystal, it can inhibit the crystallization of boric acid. These are boric acid, sulfate ion and hydrogen ion in the leaching solution, so we can recover magnesium sulfate monohydrate at high temperature and high pressure first, then crystallized boric acid at low temperature. The result is well. The recovery rate of magnesium sulfate monohydrate is up to55%and the recovery rate of boric acid up to71%. In addition, the purity of magnesium sulfate monohydrate is up to96.07%, which reach the first grade industrial products (magnesium sulfate monohydrate content up to99.5%). the purity of boric acid is up to99.55%, which reach the first grade industrial products (boric acid content up to99.4%～100.8%) according to the standard of industrial boric acid (GB538-90).In the study, we discussed the influence of the temperature, ratio of liquid to solid, quantity of alkali, the reaction time and gross pressure on leaching boron-rich slag. We obtain carbonate-alkaline optimum technological conditions with the orthogonal design experiment, carbonate-alkaline mechanism and carbonate-alkaline regulation.The leaching experiment of carbonate-alkaline results showed that the optimum sulfuric acid leaching technological conditions are:the reaction temperature135℃, the reaction time12h, gross pressure0.8MPa, ratio of liquid to solid2, stirring rate200r/min and quantity of alkali1.1time of calculation value. Under this condition, the leaching rate of Boron oxide is up to76.04%, borax yield up to71.85%. Compared with sodium carbonate, the reaction time is7h if we use mixture of sodium carbonate and sodium bicarbonate in the carbonate-alkaline experiment. We use sodium bicarbonate the time only6h in the experiment. This method decrease time and save energy. Carbon dioxide absorption and sodium bicarbonate balance are the key factors of carbonate-alkaline. We fill a small quantity of carbon dioxide in the high-pressure autoclave, the gross pressure0.8MPa, carbonate-alkaline time6h. Boron oxide leaching rate is up to76.13%and borax yield up to71.93%, borax purity up to97.37%, which fit national borax quality standard (GB/T537-1997). |
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