Study On Smelting Reduction Of Phosphate Rock React With Mixed Carbon

Phosphorus is a chemical element which is very important to both human and plants, its function is irreplaceable in many respects. As a kind of important non-renewable mineral wealth, phosphorite is generally extracted from mineral and then used to produce raw material of chemical fertilizer and chemical industry. In all kinds of phosphorite, apatite is the most common and widespread phosphorite. In China, the characteristics of the phosphorite may be concluded as follows: the reserve is very big and obviously concentrating distribution, the grade of phosphorite is very low and most of the phosphorite is collophanite, the impurity should be removed and the phosphorus is hard to be effectively used.The main technology of phosphorus chemical industry have been discussed in this paper, including phosphoric acid by wet process, phosphoric acid by furnace process and phosphoric acid by kiln process. After the comparison was made between these three processes, the conclusion of each process' s advantages and disadvantages can be made: for phosphoric acid by wet process, the whole process is very simple and easy to operate, but there are many workshop sections to be done for purification, especially, the purification for magnesium and fluorine is still a big challenge for senior engineer and the purity of phosphoric acid still cannot be really high; as to phosphoric acid by kiln process, the reaction theory is similar to phosphoric acid by furnace process, they are both a reduction reaction between carbon, silicon and phosphorite, the KPA process and the CDK process is two main process of the phosphoric acid by kiln process, the feature of this process is the special technology which used to dispose the premelting slag, we call this feature as pelletizing, whether KPA process or CDK process, the pelletizing technology is still not perfect and thus phosphoric acid by kiln process is really a good thinking but cannot be industrialized yet. Aim at the storage situation of the phosphorite in China, phosphoric acid by furnace process has been seen as the development tendency of phosphorus chemical industry, the purity of product is very high while the energy consumption is really high too. In order to solve this problem, on the one hand, smelting reduction process has been brought in from puddling for the reduction of phosphorite, and then the process of mass and heat transfer can be improved significantly; on the other hand, a lot of measure has been proposed to reduce the energy consumption, such as recovery of waste heat from furnace, addition of inorganic additives and so on.On theoretical aspect, thermomechanical analysis and calculation have been done for the reduction reaction. The study found that when the reactants in smelting reduction belongs to ingredient which has more silicon, the theoretical initial reaction temperature is 1211?; when the reactants in smelting reduction belongs to ingredient which has more calcium, the theoretical initial reaction temperature changed to be 1452?, this temperature is much higher than the other situation. Therefore, the thermomechanical analysis and calculation have proved that if the premelting slag was made up of ingredient which has more silicon, the energy consumption can be lower apparently.On this basis, effect variables in smelting reduction of low-grade phosphate ores were explored and impact of single factor on the reduction rate was analyzed. Then three main carbon source concluding active carbon, graphite and coke were chosen to be mingled as mixed reductant, analysis has been done with the reduction results. Before the experiment of each kind of mixed reductant, the physical property of each carbon source should be unequivocal, only in this way we can figure out the experimental results of the reduction of phosphorite with only one kind of carbon source and these results can be looked as reference substance for the following experiments. After this element task, the mixed reductant can be made with any two of these three carbon sources, the reduction results with this mixed carbon should be compared with the results which is reacted by only one kind of carbon source. At last, the mixed reductant was changed as a mixture of three carbon sources, as in the above case, a comparison should be done. The experiment results show that, no matter the mixed reductant is made up of two kinds of carbon source or three kinds of carbon source, the experimental results presented obviously synergistic effect, the reduction rate of phosphorite has been improved substantially, the numerical value can reach 98.7% in some case. In order to make a reasonable explanations for this synergistic effect, analysis with XRD pattern of those optimized ratio has been done. We have found that the silicon dioxide in mixed carbon source can do a better job of the fluxing function for it has formed a better Crystal form. Similarly, these tests have been done on the situation with mixed reductant made up of three carbon sources. In addition, as to the rare instances whose reduction rate became really low suddenly, we have found that the analysis of XRD pattern cannot give a reasonable explanation, so SEM photo graphs of smelting reduction samples under different magnifications have been observed to elucidate this phenomenon. From those photos, the microstructure has been changed in a large part and this change is not good for reduction reaction.