Preparation And Performance Of Reactor For Bioleaching Phosphate From High-phosphorus Iron Ore

With the further reduction of iron ore resources and the wider demand for steel, the former un-smelted high-phosphorus iron ore has been becoming the study focus and initiating the interest of many researchers in academic circles and engineering fields. This paper systematically studied the bioleaching reactor for increasing the concentration of ore slurry and decreasing the phosphates in iron ore with some samples collected from an iron ore in western Hubei province, China. This study included the design and dissolved-oxygen-recovering rate (DORR) testing of two-stages bioleaching, the mathematical models and two-stages bioleaching experiments, followed by practical design and economical analysis of this two-stages bioleaching in engineering. A novel method was put forward for solving the problem of relative low concentration ore slurry in traditional bioleaching and separating the milling processes of acid-producing and leaching for dephosphorization. In the acid-producing process, a warm surroundings was provided for Acidithiobacillus Thiooxidans (At. t) in order to reduce destroy to At. t. Meanwhile, in the stage of mineral leaching process, fluid containing At.t bacteria was used to leach the high-phosphorus iron ore at high mechanical stirring speed to decrease the sedimentation of iron particles at the bottom of reactor, resulting in the increase of phosphate removal rate. The main contents of the research and its innovation were presented as follows.In the stage of reactor fabrication:A 5 liter glass beaker was employed as the main body with inner diameter (Dn) of 18 cm and efficient depth (H) of 22 cm, a heater was surrounding the beaker, pH meter, dissolved oxygen (DO) meter and auto-controlling temperature system were equipped. An air pump with max flow rate of 6NL/min was used as circulating aeration system for providing oxygen for At.t bacteria. The inner-set circulating aeration cannel (IsCAC) with a autocontrolling diameter (dn) of 6.5cm to 9.5cm, a height (h) of 10 cm to 20 cm. The interspace between beaker and IsCAC was filled with sawdust or particles of activated carbon (PACs) as carrier for At.t bacteria. The height of sawdust or PACs was denoted as ht.In the stage of DORR testing:The relationship between h/H, ht/H, dn/Dn and aeration flux (QN) with DORR of this bioreactor was studied when no carriers were employed. The results showed that the dissolved oxygen (DO) in this bioreactor could reach saturation in 344-497s when room temperature was 11.5-17.2℃, QN was 6.67x10-5 m3/s, the h increased from 10cm to 20 cm and dn increased to 9.5 cm from 6.5 cm. At the endpoint of experiment, the DO dissolved into this bioreactor was 31.97-43.83 mg; the DORR of this reactor was relatively stable, reaching 22.01mg/m3.s-22.27mg/m3.s. For IsCAC with h=17.5 cm and dn=9.5 cm, the time of max DO concentration appearance decreased obviously with the increase of QN, but the total amount of DO did not increase. When the QN increased from 1NL/min to 6NL/min with adjacent step of 1 NL/min, the DORR was 6.82 mg/m3.s,16.42 mg/m3.s,25.99 mg/m3.s,31.33 mg/m3.s,31.57 mg/m3.s and 35.76 mg/m3.s, respectively. The DORR of this bioreactor filled with sawdust was studied further at QN of 4 NL/min. When ht=7cm,12cm and 17cm,QN=4NL/min, the temperature rose from 10.5℃to 29.6℃, the DORR of reactor decreased from 42.27mg/m3.s to 31.82mg/m3.s. Obviously, the increasing of temperature had no benefits for oxygen transmitting and oxygen dissolving into water body. When the PACs was used as carrier, the DO concentration was measured under 2 cm and 10 cm of the surface. It indicated that the DORR of this bioreactor increased to 30.47 mg/m3.s from 25.75 mg/m3.s when ht increased to 17 cm from 7 cm, but, the total DO in water decreased to 34.56 mg from 38.68 mg. It is benefit for the DO adsorption when ht less than 7 cm, but not for providing more carriers for At.t bacteria, also, it is not good for the process of acid-producing.In the stage of mathematical model building:based on Fick Law, Double-film theory and penetration theory and four basic assumptions, the model of DORR for this bioreactor was built as follows: This mathematical model was used to calculate the efficiency of oxygen transmitting (EOT) when this bioreactor was filled with no carriers at 3NL/min,h=17.5cm and H=22cm. The EOT could reach 1.62%,and then decreased. The EOT was relative low, maintaining at 0.47%-0.59%, when QN=1NL/min. The tendency of EOT for QN=2-6NL/min was very similar, rising fisrtly, then decreasing and reaching equilibrium finally. The EOT could reach 2.5% when QN=3NL/min, dn=9.5cm, h/H=0.80 at temperature of 10.5℃, but it decrased to 0.52% at 29.4℃. The change of EOT was not obvious, maintaining at 1.55% to 1.88% when this bioreactor was filled with carrier and ht/H changed from 0.32 to 0.77. But the addition of sawdust provided favourable conditions for At.t bacteria, increasing the density of microorganisms. Experimental temperatue has obvious effets on EOT. This mathematical model could be revised as the consideration of water temperatue. The EOT calculated by this model was closer to the practical EOT. After the amendment, the EOT calculated by the model was 1.25%-1.88%, but the practical EOT was 1.0%-1.6%. The main reasons were the water depth of reactor was not enough. The EOT could reach up to 10.23% when the water depth of reactor increased to 1.5 m, which reached the normal standard of EOT, 6%-12%, for air diffusion equipments used in wastewater treatment engineering.In the stage of acid-producing:Be sure to use the IsCAC as the bioreactor for our study. The basic physical parameters fo IsCAC were dn of 18cm, H of 22cm, h of 17.5cm, dn of 9.5cm, temperature of 29-30℃, QN of 4NL/min. Under the above conditions, the DORR of this reactor reached up to 27.31 mg/m3.s. Increasing the inoculum concentration of At.t bacteria from 5% to 20%, the average acid-producing rate was 1.51mmol/L.d to 5.81 mmol/L.d. And the acid-producing rate increased from 1.57 mmol/L.d to 4.23mmol/L.d when ht/H increased to 0.77 from 0, but the acid-producing rate had no obvious rise when ht/H>0.55. And the acid-producing rate rose to 5.51 mmol/L.d from 0.36 mmol/L.d when the QN increased from 1 NL/min to 6 NL/min, but it also had no obvious variations when the QN>4 NL/min. Meanwhile, the relationship between hydrolic retention time (HRT) and acid-producing of At.t bacteria was also studied. From the continuous experimental data of 9 days, it showed that the acid-producing rate reached up to 5.81-16.59mmol/L.d when the HRT was 14 days.In the stage of leaching:Solution with ph=1.0 or so was chose, the leching experiments were made for raw ore and concentrate respectively. When raw ore used as experimental sample, the content of phosphate decreased to 0.17% and grade of ore reached 44.64% when leached for 12 h, the optimal experiment results appeared at the leaching time of 18 h. It seemed the content of phosphate in residue of mine rose with further increasing leaching time. The grade of ore decreased by 2.63% from 58.41% and the content of phosphate in mine residue increased to 0.35% from 0.1% when the contentration of mine increased from 1% to 4%. But the phosphate content was 0.24%, less than 0.25%, when the concentration of mine was less than 3%. It had obvious effects to the enhancement of mine grade when the acid solution contained some At.t bacteria, but it had no obvious effects to the degradation of phosphate in the residue. The grade of mine reached up to 46.64% when solution contained some At.t bacteria at concentration of 2%, but the mine grade was only 45.2% when it was leached for 18% with no At.t bacteria solution. It showed that the existence of At.t bacteria had some obvious effects to raise the mine grade and decrease the content of phosphate in the residue. Meanwhile, the SEM and XRD were used for analyzing the sulphate powder after being leached by solution contained At.t bacteria, but the effects were no obvious. It indicated that the At.t bacteria only used the sulphur powder as energy materials and produce sulphuric acid, no making the sulphuric powder into other matters, which was the result expected in our experiments. The SEM results showed that the surface of sulphuric powder become coarse and hydrophilic seemed from the outside of this powder. The pattern of SEM witht 10000 time showed that the surface of sulpharuic powder had some obvious etched hole which seemed as the results affected by At.t bacillus. At the same time, The XRD and SEM were also used to analysis the raw ore, concentrate and some samples of them treated by At.t bacillus. The main ingredients of magnetic concentrate were magnetite, hematite (γ-Fe2O3) and quartz. The ingredients of raw ore did not change, still were hematite (γ-Fe2O3) and quartz, after it was leached by At.t bacillus, and no ferrovanadium sediment were found in this products. This phenomenon also occurred in the concentrate when it was leached by At.t bacillus, the main ingredients of concentrate were magnetite, hematite (γ-Fe2O3) and quartz still. The results of SEM patterns showed that the raw ore and concentrates gathered into scaly, the reason maybe the relative single element and iron gathered after the phosphate and some other impurities were eliminated by At.t bacillus in the bioleaching process.Process concept for two-stage bioleaching dephosphorization:On the scale of 300 liter acid solution containing At.t bacteria for one day, the solution contained 15 mol H2SO4, each additional H2SO4 costs 1.64 Yuan. The costs for decreasing phosphate from 1.1%to 0.15% for 1 kg raw ore was 2.14 Yuan, which was relative higher than the chemical dephosphorization. The main reason was the concentration of ore slurry was too low (4%). If we only expected to reduce phosphate to 0.3% in the raw ore, the concentration of ore slurry could rise to 8%,22.84 kg ore could be dephosphorized for one day, causing the costs decrease to 1.07 Yuan for one kg raw ore.The innovation of this paper was as follows:A Ultilizing At. t bacteria has characteristics of utilizing low valent sulphur as energy matters to produce sulphur acid, then sulphuric acid was used to leach phosphate from iron ore with high content of phosphate. Two-steps bioleaching process was put forward to reduce the phosphorus content in iron ores.B Design a reasonable, high efficient inner cycle bioleaching rector, the inside structure and DORR function were tested and valued, main points were on the charge for the efficiency and structure of the reactor.C. The phosphoric bioleaching rate was reached up to 75%, the residue phosphorus in the treated ore was only 0.15%, and the iron grade was 56.49%. Based on the results of this experiment, the cleaner craft was presented, also the on-line monitoring system was established which provided a fine growth surroundings for At.t bacteria.