【作者】 皮科武；

【导师】 龚文琪；

【作者基本信息】 武汉理工大学 ， 矿物加工工程， 2010， 博士

【摘要】 随着铁矿资源的进一步减少和社会对钢铁需求量的进一步扩大,以往无法冶炼的高磷铁矿逐渐成为研究和开发的热点,越来越受到学术界和工程界的重视。本文以湖北某高磷铁矿为研究对象,以降低其磷含量为主要目的,系统地开展了从生物降磷反应器的设计与复氧性能测试、反应器曝气复氧数学模型的建立和两步法生物降磷浸矿实验,到两步法生物降磷工艺的设计与经济分析的理论与实验研究,提出一种可解决微生物浸矿时矿浆浓度过低,细菌产酸与浸矿过程无法独立进行的两步浸矿新方法。该方法将嗜酸氧化硫硫杆菌(At.t菌)产酸过程与其所产酸用于浸矿除磷分开进行,在产酸阶段为At.t菌提供温和的生存环境,减少外界对At.t菌生长过程的破坏；在浸矿阶段则利用产酸段产生的酸性菌液以较高的机械混合方式将矿石与菌液混合,达到使矿石分散悬浮于菌液中的目的,减少矿石在反应器底部的沉积,从而提高矿石中磷的去除率。本论文主要研究内容及取得的成果包括以下几个方面：1.生物反应器制作以5L玻璃烧杯为反应器主体,在其外部设置保温与加热装置,安置pH值测定仪,DO测定仪和温度自动设定与控制装置,采用内循环气动搅拌方式为主,通过空气泵向反应器曝气以提供微生物生长所需的氧气。反应器直径Dn=18cm,内部流体深度H=22cm,内置循环曝气筒直径dn在6.5cm-9.5cm内可调,高度h可调范围为10cm-20cm,内置循环曝气筒与反应器内壁间可用载体(如木屑、活性炭等)进行填充,载体填充高度用ht表示,以形成内置载体的内循环生物反应器。2.反应器复氧性能测试At.t菌的生长需消耗溶解氧,生物反应器能否为At.t菌提供充足的溶解氧是评价反应器性能好坏的重要指标,因此提高反应器对氧的利用率是降低反应器能耗的主要措施。当反应器内无生物载体时,研究了h/H, ht/H, dn/Dn的变化及曝气量QN对反应器复氧性能的影响。实验发现,当反应器内流体体积为4.0 L,实验温度T在11.5-17.2℃,曝气量QN=6.67×10-5m3/s,内置循环曝气筒的高度h从10cm逐渐增加到20cm,直径dn由6.5cm逐渐增加到9.5cm时,在344s-497s内均能使反应器内溶解氧达到稳定且接近饱和,溶入流体中的溶解氧的量为31.97mg-43.83mg,反应器在此时段内的平均复氧速率为22.01mg/m3.s-22.27mg/m3.s,复氧速率相对稳定,反应器不同层面上DO为10.5-11.3mg/L。对h=17.5cm、dn=9.5cm的内置曝气筒,随QN增大,反应器内最高溶解氧出现的时间明显缩短,但溶解氧总量不一定增加。当QN从1NL/min(1.66×10-5m3/s)增加到6NL/min(10×10-5m3/s)时(每次增加1NL/min),反应器的复氧速率分别为6.82mg/m3.s、16.42mg/m3.s、25.99 mg/m3.s、31.33mg/m3.s、31.57 mg/m3.s和35.76 mg/m3.s,QN在3-5 NL/min时反应器复氧速率相对理想。当反应器内填充木屑时,进一步研究了木屑填充高度ht对反应器复氧性能的影响,当ht分别为7cm、12cm和17cm,控制QN=4NL/min,温度从10.5～C上升到29.6℃时,反应器复氧速率由42.27mg/m3.s下降到31.82mg/m3.s,显然反应器内温度的上升不利于氧的吸收。当反应器内填充颗粒活性炭时,就反应器液面下2cm和10cm处的溶解氧进行了测定,结果表明当ht从7cm增加到17cm时,反应器的平均复氧速率由25.75 mg/m3.s增加至30.47 mg/m3.s,但反应器内溶解氧总量从38.68mg下降到34.56mg。ht为7cm及以下有利于氧的吸收,但反应器内填料过少不利于向At.t菌提供栖息的载体,也不利于At.t菌的产酸。3.反应器复氧数学模型的建立以Fick扩散定律,双膜理论和渗透理论为基础,通过四点基本假设,在实验结果的基础上,建立反应器的氧瞬时传质速率模型为：应用该数学模型就反应器对氧的利用效率进行了验证和计算。当反应器内无载体,QN=3NL/min,h=17.5cm和H=22cm时,反应器对氧的利用效率逐渐增加到1.62%,然后下降。加大曝气量反应器对氧的利用效率首先增加,然后减小,当QN=1NL/min时,反应器对氧的利用效率相对较低,基本维持在0.47%-0.59%。当QN在2NL/min至6NL/min时,反应器对氧利用效率的变化趋势基本相同,首先增加,然后随曝气时间延长逐渐减小,到后期基本趋于稳定。当QN=3NL/min, dn=9.5cm,h/H=0.80,温度为10.5℃时,反应器对氧的利用率可达2.5%,当实验温度上升到29.4℃时,反应器对氧的利用率下降为0.52%。反应器内添加木屑后,反应器对氧的利用效率变化不大,当ht/H从0.33上升到0.77时,反应器对氧的利用效率在1.55%-1.88%,但内设置木屑可为微生物的生长与栖息创造良好的条件,增加反应器内微生物密度。实验温度对氧传质速率模型有一定的影响,对反应器复氧数学模型进行温度影响的修正后,其模型的表达式为：氧的利用效率更加接近于反应器对氧的实际利用效率。经过温度修正后,反应器对氧的实际利用效率基本在1.0%-1.6%,而氧传质模型计算的氧理论利用效率为1.25%-1.88%,产生两者差距的主要原因是反应器内水深不够。当反应器水深达1.5m时,反应器对氧的利用效率可达10.23%,完全可达到目前空气扩散装置的氧转移效率6%-12%的水平。4.反应器产酸效果实验确定采用内置载体的内循环方式反应器进行产酸反应,产酸反应器基本物理参数为：内径Dn=18cm,液面高度H=22cm,内置曝气循环曝气筒h=17.5cm、内径dn=9.5cm,反应温度控制在29-30℃,当QN=4NL/min时,反应器复氧速率可达27.31 mg/m3.S。当At.t菌接种量由5%增加到20%时,在培养时间内反应器的平均产酸速率为从1.51mmol/L.d增加到5.81mmol/L.d,当ht/H从0逐渐增加到0.77,反应器产酸速率从1.57 mmol/L.d增加到4.23 mmol/L.d,但当ht/H大于0.55后,反应器产酸速率增加不很明显。曝气量QN从1NL/min增加6NL/min,反应器的产酸速率可从0.36 mmol/L.d增加到5.51 mmol/L.d,但在QN大于4NL/min后,反应器产酸速率增加幅度不明显。同时考察了菌液水力停留时间(HRT)对At.t菌产酸速率的影响,HRT为14d时,At.t菌产酸速率相对理想,在5.81-16.59mmol/L.d之间,但变化幅度较大。5.浸矿效果研究选取pH值为1.0左右的菌液,分别对原矿及精矿进行了浸矿实验。采用原矿作为实验矿石,当浸矿时间达到12h后,矿石中磷的含量为0.17%,铁的品位为44.64%,浸矿最佳效果出现在浸矿时间达到18h时,再继续延长浸矿时间,滤渣中磷的含量有上升的趋势。采用精矿作为实验矿石,当矿浆浓度从1%增加到4%时,铁的品位从58.41%下降了2.63%,浸矿渣中磷的含量从0.1%上升到0.35%；但当矿浆浓度低于3%时,滤渣中磷的含量最高为0.24%,低于0.25%。菌液中是否存在At.t菌对提高铁的品位和降低矿石中磷的含量影响不大,当矿浆浓度为2%,以原矿为对象用含At.t菌的菌液浸矿12h后,铁的品位为44.64%,浸矿渣中磷含量为0.17%,用不含At.t菌的菌液进行浸矿12h后,铁的品位为44.58%,浸矿渣中磷含量为0.18%。同时对硫粉及矿石进行XRD和SEM分析,硫粉通过At.t菌作用前后变化不大,这说明At.t菌只利用硫粉作为能源物质产生硫酸,而没有将硫粉转变为其它固体物质。SEM分析发现,通过At.t菌作用后硫粉的表面变得粗糙,10000倍SEM图片显示其表面有明显的浸蚀坑,类似于杆菌作用的效果。矿石XRD和SEM分析表明,磁选精矿的主要成份为磁铁矿、磁性赤铁矿(γ-Fe2O3)和石英,通过At.t菌作用后也未发现铁钒类沉淀产生,其主要成分仍然为磁铁矿、磁性赤铁矿和石英；原矿通过At.t菌作用后其成分仍然为赤铁矿和石英,未发现铁钒类沉淀产生。SEM分析结果表明,At.t菌作用精矿(原矿)除磷后出现了成片聚集成鱼鳞状,其原因可能是矿石中磷及其它杂质被At.t菌作用后含量下降,矿石品位上升后产生聚积所致。6.两步法生物降磷工艺按日产300L(pH=1.0)菌液计算,菌液中所含H2S04的量为15 mol,则每摩尔硫酸生产成本为1.64元。将lkg含磷量为1.1%的铁矿石中的磷降低到0.15%的成本为2.14元,成本相对较高,主要原因是矿浆浓度过低(4%)。若设计只将P降低至0.3%,则矿浆浓度可达8%,每日可浸出铁矿石为22.84kg,每浸出lkg矿石成本为1.07元,显然如何进一步提高生物选矿中矿浆浓度对降低生产成本至关重要。本文创新之处在于：A、利用At.t菌具有以低价态硫作为能源物质产生硫酸,然后利用硫酸将铁矿石中磷溶解浸出,提出两步法生物作用降低高磷铁矿石中磷的思路；B、设计了合理、高复氧速率的内循环生物反应器,对反应器内部结构与性能进行测试与评价,重点研究了复氧速率与反应器结构的关系,建立了反应器氧瞬时传质速率数学模型；C、反应器所产生的酸性菌液对铁矿石除磷效率达75%,精矿粉中残余磷含量最低可达0.1%,铁品位为58.41%,就反应过程及实验结论,设计了两步法生物降磷的清洁生产工艺,构建了相应的在线监控系统,为浸矿生物的生长过程提供了最佳的条件。更多还原

【Abstract】 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.更多还原