Study On Process Condition And Kinetics Of Low-grade Phosphate Ore By Smelting Reduction Technology

With the progress of human society, energy problem becomes more and moreseriously. Under the framework of the construction of a conservation-oriented society,circular economy has a decisive role position. Phosphate ore as one of the non-renewablemineral resources, is the basic raw material for agricultural production and phosphoruschemical industry. It is widely used in the field of fertilizer production, chemical industry,metallurgy industry and sophisticated technology. Therefore how to effectively useLow-grade phosphate ore, saving energy is worthy of attention with the development of thenew age.At present, there are three traditional methods for preparing phosphoric acid: the wetacid process, the thermal process, and the kiln phosphoric acid process. The wet acidprocess uses the inorganic acid such as sulfuric acid, hydrochloric acid, nitric acid todecompose phosphate ore in order to produce phosphoric acid. The process requires highgrade phosphate ore, the production of phosphoric acid concentration is low, and has highimpurity content. What’s more the main technical difficulities is purification technology.In the thermal process, phosphate ore reduced by coke to prepare phosphorus steam whichthen through combustion and hydration to produce phosphoric acid in a furnace or a blastfurnace. This process of phosphoric acid of high purity but large power consumption, andblast furnace process has dedusting problem which will pollute the environment. Thereaction principle of kiln phosphoric acid process is the same as the thermal process. Thereduction and oxidation of phosphate rock are in the same device. This process has lesspower consumption, use Low-grade phosphate ore, no sulfur, which is very accord withChinese phosphate grade conditions. However phosphorus mixture balling technology,easy to knot and block, and structure and material requirements of the equipment is high,so it cannot e industrial amplification.Smelting reduction method refers that adding a certain proportion of phosphorus ore, silica, carbon into melting furnace for reduction and oxidation. The method makes thereduction and oxidation of phosphate rock is carried out in the same reactor, and can makefull use of heat generated by the combustion of phosphorus to supply reduction reactionitself. The concentration of product of this process is high, the equipment is simple, andmake full use of Low-grade phosphate rock. So melting reduction process for phosphoricacid has a huge space for development. In view of this, we studied on melting reduction ofmiddle-low grade phosphate rock for a series of researches.Firstly, we studied the technological conditions of smelting reduction of low-gradephosphate ore using the laboratory high temperature electric furnace. The effects ofreaction temperature, reaction time, the consumption of carbon, the basicity of phosphateore on P₂O₅reduction rate were studied. The results showed that the P₂O₅reduction rateincreases with the increase of temperature, reaction time, the consumption of carbon.While the P₂O₅reduction rate increases at first, then decreases and becomes stable at lastwith the increase of the basicity of phosphate ore. P₂O₅reduction rate reached themaximum value of98.93%when B=0.9. So the suitable reaction conditions of this processwas for the temperature1550℃, reaction time60min, two times carbon amount of thetheoretical value, B=0.9.Secondly, orthogonal experiment was designed to further optimization of reactionconditions. The optimal conditions and the single factor experiment results are basicallythe same, only with a little differences in basicity which changed from0.9to1.1. This timethe reduction rate of P₂O₅reached98.12%, once again proved that the basicity in the rangeof0.9-1.1had little effect on the experiment.Finally, The relationship of P₂O₅reduction rate and time under the condition of threedifferent basicities and temperatures were studied to further explore dynamics of thisreaction. The results show that the reaction is first-order reaction in terms of basicity andlinear fitting is good. At the same time, the apparent activation energy decreased alongwith the increasing of basicity. This experiment provides the basic data for the futuredevelopment of the industry.