| With the continuous mining of iron ore,an increasing number of lean ore and refractory ore were obtained.In order to guarantee the grade and recovery rate of iron,for one hand,grinding fineness was increased to achieve the monomer separation of mineral and for the other hand,the depressing agent dosage of starch was increased to improve the separation efficiency of useful ore,which would cause fine particle size and high viscosity of ore pulp.Too fine granularity would enhance the blocking of filter cloth and decrease cake permeability,and change the capillary forces inside cakes,leading to the formation of shrinkage cracks and affecting the normal running of filtration equipments.The high viscosity of ore pulp would also decrease the capacity of filters and increase cake moisture.Therefore,studies on the cake cracking during dewatering process and worse filterability of roasting-low intensity magnetic separation(LIMS for short)iron concentrates from a certain dressing plant in Gansu province were conducted in this paper,which might provide theoretical basis and experimental evidence for solving problems in ore dressing industry.Firstly,the formation process,influence factors and common countermeasures of shrinkage cracks were analysed.Capillary forces were found to be the immanent cause account for shrinkage cracks based on the analysis of liquid bridge model.Meanwhile,it was also found that particle contact angle and liquid surface tension accounted for a larger proportion in the derived capillary force equation after the analysis of loading process.The adsorption behavior of a cationic surfactant cetyl trimethyl ammonium bromide(CTAB)on sample particle surface was studied from the perspective of decreasing capillary forces and the improvement effect of CTAB on shrinkage cracks of LIMS iron concentrate cakes was verified by using a bench-scale pressure filter.The analysis shows that CTAB molecules absorb on particle surface mainly by electrostatic attraction,according with BET multi-molecular adsorption model.When the solid and CTAB concentration of the tested suspension are 200 g/L and 120 mg/L,respectively,the contact angle of particles reaches a maximum of 85.05° and the surface tension of filtrate is 46.77 mN/m with a drop of 21.73 mN/m,and capillary forces will decrease to about one-sixth of the original value.Cracking begins until differential pressure reaches 0.3 MPa.Compared to cakes without CTAB coating,the crack parameters of modified cakes have an obvious improvement,despite the occurrence of cracks after 0.3 MPa.Regarding the problems of low filtration rate and high cake moisture of LIMS iron concentrates,the influence mechanism of particle properties on filtration rate and cake moisture was analyzed,and various flocculants,surfactants and their complexes were adopted to improve the filterability from the perspectives of improving particle refinement and solid-liquid interaction forces.The effect and mechanism of different kinds of chemical filter aids on the filterability of iron concentrates were verified by using a modified vacuum filtration apparatus.The experimental results show that organic polymer flocculants enhance the permeability of filter cakes by forcing fine particles to form flocs via adsorption and bridging,solving the problem of fine granularity and thus increasing filtration rate.Surfactants are able to decrease capillary pressure by decreasing the air/water surface tension and the wettability of particles,improving the problem of interfacial properties and reducing cake moisture.With the compounding use of flocculants and surfactants,higher filtration rate and lower cake moisture can be obtained. |
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