Study On Carbothermal Reduction Kinetics And Element Distribution Of Black Tungsten Slag

Tungsten slag is a solid waste generated during the production of APT by alkali pressure cooking.In 2016,the harmless treatment of tungsten slag became a major problem to be solved after tungsten slag was included in the’National Hazardous Waste List’.Because the harmful elements such as arsenic and lead in tungsten slag exceed the standard,and the tungsten slag contains a variety of valuable metals and the content is higher than that of some concentrates,it is necessary to take into account the comprehensive recovery of valuable metals in tungsten slag and the balance of harmless treatment.At present,the preparation of alloy from tungsten slag by carbothermal reduction consumes a large amount of stored tungsten slag,making tungsten slag a general solid waste,and recovering valuable metals in tungsten slag to produce economic benefits is a three-pronged approach.The properties of Fe O-Mn O-Ca O-Mg O-Si O₂-Al₂O₃six-element slag system were studied by Factsage thermodynamic software,and the activity and activity coefficient of Fe O and Mn O were calculated respectively.Tungsten slag with high content of valuable metals was used as the experimental raw material,graphite was used as the reducing agent,and the carbothermic reduction experiment of tungsten slag was completed by electric furnace.The isothermal reduction reaction kinetics of tungsten slag and the distribution of iron,manganese,tungsten,niobium,tin,arsenic,lead and bismuth in the alloy phase,slag phase and gas phase were studied.The effects of temperature and binary alkalinity were investigated.The conclusions are as follows:（1）The initial melting temperature and complete melting temperature of slag system increase with the increase of binary basicity in the range of 0.7～2.0.The binary basicity is 1.3～1.7,and the temperature is 1623～1873 K.The viscosity of slag decreases with the increase of temperature,and increases with the increase of binary basicity.The activities and corresponding activity coefficients of Fe O and Mn O in the slag were calculated when the binary basicity was 0.7～2.0,α_{Fe O}decreased with the increase of basicity,andα_{Mn O}increased with the increase of binary basicity.（2）The reduction degree of black tungsten slag increases with the increase of reduction temperature.The reduction rate first increases rapidly,then decreases rapidly,and finally tends to be stable.When the reduction temperature is 1673～1873K and the reaction time is 60 min,the apparent reduction degree of the black tungsten slag increases from 27.40%to 70.54%with the increase of the reduction temperature.The reduction degrees of iron,manganese,tungsten and niobium in the black tungsten slag are 93.18%,38.94%,94.07%and 84.10%,respectively.The reaction time of 0～12.5 min is the control stage of interfacial chemical reaction.The reduction degree of black tungsten slag increases rapidly with time,and the apparent activation energy of reduction reaction is 137.30 k J·mol^-1.The reaction time of 30～60 min is the diffusion control stage,and the reduction degree of black tungsten slag increases slowly.This stage is the diffusion control stage,and the apparent activation energy is573.92 k J·mol^-1.（3）When the temperature increases from 1723 K to 1873 K,the alloying rate of valuable metals increases.The best reduction temperature in the experiment is 1823K.Carbothermal reduction of wolframite slag recovers most of iron,tungsten,tin and niobium and recovers about 40%of manganese.About 40%of arsenic enters the alloy and 40%of arsenic volatilizes into the gas phase.Most of lead and bismuth volatilize into the gas phase,and a small part of lead and bismuth enter the alloy.When the binary basicity increases from 1.3 to 1.7,the alloying rate of valuable metals decreases.When the binary basicity is 1.3～1.5,the alloying rate of valuable metals is higher.The alloying rates of iron,manganese,tungsten,tin and niobium are about 90%,40%,95%,90%and 85%,respectively.When the binary basicity is 1.6～1.7,the alloying rate of iron,manganese,tungsten,tin and niobium decreases.The best binary basicity range is 1.3～1.5.With the increase of binary alkalinity,the alloying rates of arsenic and lead are 40～66%and 18～26%,respectively,and85%of bismuth volatilizes into the gas phase.