| Mn-Zn ferrites are significant ceramic materials applied extensively in transformers, magnetic recording heads, information storage systems, medical diagnostics and biomedicine, due to their excellent properties such as high magnetic permeability, high saturation magnetization, high dielectric resistivity and low power losses. With the development of modern electronic and telecommunications industry, more than300,000tons of Mn-Zn ferrites have been annually produced since2010in China. This has resulted large amount of waste from discarded Mn-Zn ferrites and grinding products from preparation and processing of the soft ferrites. Some of the wastes are incinerated or buried together with municipal domestic waste; some others are exposed to the nature by simple disposal. Because of the high grades of iron, zinc and manganese, effective utilization of Mn-Zn ferrite wastes has thus become an attractive study from the viewpoint of environmental preservation, resource saving and waste volume reduction. A novel recycling route using hydrometallurgical route and traditional ceramic process was applied to process the Mn-Zn ferrite wastes and prepare the corresponding power loss soft magnetic product. The research contents and results are as follows.Hydrometallurgical route including acid leaching, co-precipitation, boiling refluxing synthesis, purification, was used to recycle the wastes and prepare the Mn-Zn ferrite powers. Based on the growth unit model of anion coordination polyhedron, the benifical growth units Zn(OH)42-、Mn(OH)42-and Fe(OH)4-were investigated in the system of Fe(Ⅲ)-Mn(Ⅱ)-Zn(Ⅱ)-NaOH-H2O. The optimal hydrometallurgical preparation conditions were deterimined. Almost98%of Fe, Mn, Zn in the waste materials could be extracted on the conditions of leaching time3.0h, at Experimental/Theoretical dosage ratio1.15, reaction temperature95℃with liquid/solid ratio4:1. The co-precipitation efficiency of Fe, Mn, Zn using NaOH as precipitant was98.3%,95.9%and95.4%, respectively on the conditions of pH10.0-13.0, agitation speed300rpm, reaction time1.5h. The optimal boiling refluxing synthesis conditions of co-precipitation pH12and synthesis time3.0h were determined through theoretical analysis and experiment confirmation. The chemical composition (Fe48.01%, Mn16.14%, Zn6.23%), XRD and FT-IR suggested the prepared particals had higher degree of transformation and better crystallizations. The acid concentration of0.5%HNO3+1.0%HAc was carried out to remove the imputities and the purified ferrite powders had low impurities contents (SiO20.0092%, CaO0.007%, Al2O30.012%, MgO0.005%), which satisfied the requirement of industrial Mn-Zn ferrite powers.Traditional ceramic process using synthesized powders was conducted to prepare power loss Mn-Zn ferrite product. The optimical conditions and steps relevant to this process were followed:(i) pre-sintering in the in the muffle at900℃for3.0h,(ii) doping with CaCO3(0.02%), ZrO2(0.02%), V2O5(0.02%), Nb2O5(0.02%),(iii) milling for7.0h in the dual planetary ball mills,(iv) manual granulation with10%PVA,(v) forming a circle (Φ30×Φ18×9mm) with compacting pressure15Mpa using hydraulic press, and (vi) calcining in the sintering elevator furnace at1300℃for4.0h with3.6%partial pressure of oxygen,(vii) cooling with the controlled atmosphere in accordance to the formula1gPo2=-14540/T+7.8.The comprehensive performances of Mn-Zn power loss ferrite in the present study were initial permeability (μi=2654), power loss (Pcv=644kW·m-3,25℃), saturation flux density (Bs=476mT), curie temperature (TC=243℃), which can complete with P41made in Acme Electronics Corporation of Taiwan. |
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