High phosphorus oolitic hematite is a typical refractory iron ore, which is widely distributed all over the world. It has the characteristics of low iron grade (35%-50%), high phosphorus content (0.4%-1.8%), fine distribution, etc., which may be related to the difficulty of quality improvement and dephosphorization.Phosphorus in oolitic hematite mainly exists in the form of hydroxyapatite, fluoroapatite and chloroapatite, which are difficult to remove by traditional beneficiation. Therefore, phosphorus removal from oolitic iron ore has been paid more and more attention. Many research methods have been reported in previous studies including froth flotation, acid leaching, direct reduction, etc.
Froth flotation can reduce the phosphorus content in Brazilian hematite from 0.82% to 0.37% with 150 g/t of Flotigam EDA (an amine collector). Although foam flotation can achieve dephosphorization to a certain extent, it also has disadvantages such as large loss of iron resources and improvement of iron grade. Studies have shown that acid leaching of high phosphorus iron ore can reduce the phosphorus content to less than 0.05%. Besides high cost, it also creates serious pollution problems. Bioleaching can obtain a high dephosphorization rate, but the leaching time is long and the preparation of bacteria is time-consuming, which limits its application in the iron ore industry. Therefore, some studies have focused on direct reduction and magnetization roasting to remove phosphorus from ores.
In recent years, the coal-based direct reduction-wet magnetic separation process has been used to upgrade oolitic hematite. In a study by Kokal et al., HPOHO (49.50% Fe and 0.75% P) was roasted at 900 °C for 20 min and the crude concentrate was leached after magnetic separation in 3% dilute sulfuric acid for 1 h. The phosphorus content can be reduced to less than 0.2%, the concentrate iron grade is 59.9%, and the iron recovery rate is 97%. Note that the iron concentrate with 89.63% Fe and 96.21% Fe recovery was obtained from oolitic hematite ore, reduced at 1250 °C for 50 min at 42.21% Fe and 1.31% P. However, the dephosphorylation rate was low, which is consistent with other studies. . Direct reduction is an effective method for separating iron and phosphorus from oolitic hematite. However, the amount of reducing agent needed is large, the reduction time is very long, and the energy consumption and operation cost are high.
This paper proposes a new method for iron-rich phosphorus removal from oolitic hematite: sodium magnetization roasting-wet magnetic separation-acid-base leaching process. In this process, sodium hydroxide is used during roasting to enhance the reduction of iron-bearing minerals and the removal of phosphorus.
Only using traditional magnetization roasting-magnetic separation, iron concentrate contains 57.49% Fe, P 2 O 5 1.4% iron recovery rate is 87.5%, and dephosphorization rate is 34.27%, which shows that the traditional magnetization roasting-magnetic separation process is difficult to remove iron Effective dephosphorization and upgrading. The obtained crude magnetic concentrate was then subjected to acid leaching and alkali leaching steps, and the final product with an iron content of 64.11% and a P2O5 content of 0.097% was successfully manufactured. In addition, the addition of NaOH can promote the mineral phase reconstruction of Al- and Si-containing minerals during the magnetization roasting process, strengthen the upgrading of iron, and promote the growth of iron grains.
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