Cold Consolidation Of Pellets Direct Reduction Technology And Its Applications

The fundamental theories on cold-bonded pellet coal-based direct reduction have been studied systematically by using XRD, SEM, electron microscopy, energy spectrograph ect,which offer a great progress for application of cold-bonded pellet direct reduction. Furthermore, the recovery of value elements from zinc-leaching residue has been performed successfully with this technique.The systematical investigation on ferrous concentrate cold-bonded pellet preparation, heat properties and direct-reduction mechanism has been carried out according to the principles of high-molecular compound chemistry, surface chemistry, catalytic theory etc. The results show: the binder F with function of adhesion,catalyst and reduction brings successfully out the replacement of high-temperature oxide bond (1200#~1300#) by low-temperature bond (200#~250#) and cuts high-temperature process through. The strength of cold-bonded pellet of impact strength 212N~248.3N, drop strength 4.4 times/lm~5.8 times/lm every pellet, abrasion strength(-3mm) 0.8%~1.3% can be obtained under conditions of 1.5% F , 5min~6min mixture damp grinding pretreatment, the moisture of balling 8.0%~8.5% and balling time 20min , bond temperature 200#~250#,wind current rate 1.2m/s~1.5m/s, bond time 20min~25min.The heat properties of cold-bonded pellet with F binder have been studied by using electron microscopy, SEM and XRD . The results show: there is no crystal transformation or anisotropy during the reduction of magnetite. What's more, the volume contracts (reducing swelling ratio is -3.24%).The cold-bonded pellet with porous, good reducing properties and quick formation of ferrum has good heat strength in reducing process.But when a large number of ferrous oxides appear (800#~900#), of pellet strength reduces. In order to improve heat strength of cold-bonded pellet between 400# and 950# during reducing course, a new complex binder has been developed through composition of organic binder and inorganic binder. When compound condition is : 1.5%F, 0.86%A, 0.7% bentonite, the strength of cold-bonded pellet as follows: impact strength 480N, drop strength 6.6 times/lm ,abrasion strength(-3mm) 0.5%, the lowest strength during direct reduction course surpasses 200N. XRD results show: the complex binder increases d (interplanar spacing), accelerates the reduction of ferrous oxide and raises heat strength of cold-bonded pellet effectively.The study of cold-bonded pellet direct reduction mechanism shows: owing to high void ratio, with composite binder, cold-bonded pellet reducing reaction as volume reaction model. Under 800'C,the reaction is controlled by surface chemistry reaction. Above 900, by diffusion. Between 800~900,by mixture control.The enrichment and recovery of Zn, Fe, Ga, Ge, Ag have been realized by cold-bonded briquette pellet direct reduction technique from Zinc-leaching residues. The strength of cold-bonded pellet is as follows: impact strength 54.2 X 105Pa ,drop strength 19.2 times /1m, the lowest heat strength is above 35 X 105Pa during reducing course under conditions of C-5 binder 5%, pressure 255 X 105Pa and moisture 17.5%. The XRD results show that the main minerals such as FeO, ZnS, Zn2SiO4, ZnS (hexahedron), ZnO and P -Zn2SiO4 have been formed when pellets are reduced 20 min at 900 During reduction the formation of iron oxides and silicate sustains good heat strength. With reduction time prolonging at 1000, the volatilization of zinc increases, the iron oxide is reduced and metallic iron forms and the heat strength of pellet is improved obviously because of the formation of metallic iron.The new process of reducing roasting and magnetic separation has been applied to treat zinc-leaching residues bearing Fe 21.18%, Zn 18.6%, Ga 527g/t, Ge 305g/t, Ag 508g/t .The metallization of iron is 95.10%, recovery of Ga is 89.1% and volatilization of Zn is 98.42% when reduction time is ISOmin at 1100. After crush, grind and separation of the reducing roasting residues, the obtained magnetic product has Fe90.16%, Ga 2164g/t and Ge 1410g/t, the recovery of Fe, G...