Exploitation Of Composite Binder Used For Cold-Pressed Carboniron-Bearing Dust And Sludge Pellets And Its Mechanism

Iron-bearing dust and sludge is a large amount of solid waste with high iron content produced in during the steel production process.Coal-based direct reduction technology based on China's energy structure is one of the effective ways to dispose the iron-bearing dust and sludge.In order to ensure the agglomeration strength of iron-bearing dust and sludge,the binder is usually introduced.However,as the most of the current binders used for agglomeration are a single type,the strength of agglomeration is difficult to meet the production requirements,and the metallization rate of the reduction product needs to be further improved.Therefore,the exploitation of agglomerating binder for iron-bearing dust and sludge with excellent properties has become an important issue to be solved urgently,which will have practical significance for realizing the internal circulation utilization of iron-bearing dust and sludge.In this paper,the influence of binder types and addition amounts on the cold strength of the carbon-iron-bearing dust and sludge pellets were experimentally investigated.The results showed that compared with inorganic binders,the liquid-phase bonding and bridging ability of the solid particles inside the dust and sludge provided by a single type of organic binders is relatively stronger,and the green pellets have excellent resistance to high-speed shear.Among them,the drop strength of the pellets with the organic binder G is at a relatively high level,which exceeds 24 times/0.5m with using 4%binder G.Based on the cold strength data of pellets with using a single type of binder,two composite binders G-RH and G-AC are optimally selected.The drop strength of G-RH and G-AC pellets is>24 times/0.5m and 21.0 times/0.5m respectively,which are higher than the drop strength of the reference ZJ pellets(15.6times/0.5m).In addition,compared with ZJ pellets,the compressive strength and dry strength of G-RH and G-AC pellets are increased by 83.2%,36.3%,97.5%and 93.4%,respectively.Combined with the FTIR analyses and rheological analyses of the binder,it is believed that the improvement effect of the composite binder on the strength of the dust and sludge pellets is from the synergistic effect of the inorganic and organic components inside the binders.Organic components are chemically adsorbed on the surface of carbon-iron-bearing dust and sludge particles through carboxylate(-COO^-).The inorganic component RH is hydrolyzed to form a gelling phosphate hydration phase.After AC hydration,colloids such as Al₂O₃·nH₂O,aluminum glue(AH₃),and calcium aluminate decahydrate(CAH₁₀)are precipitated.The consolidation effect of the pellets is enhanced by a continuous liquid-phase bonding bridge formed bwtween the macromolecular structure of the organic component G and the hydration product of the inorganic component.The high temperature roasting reduction of carbon-iron-bearing dust and sludge pellets showed that the reduction rates of the pellets with G-RH and G-AC composite binders are close in the temperature range of 1100?to 1250?,and the reduction degradation rate is lower than the reference ZJ pellets.The metallization rate of G-AC pellets reduced at 1250?for 35 min is approximately 90.2%,which is significantly higher than the that of ZJ pellets(81.9%).The high temperature phase reconstruction of the inorganic components inside the composite binder ensures the stability of the pellet structure during the reduction process,which is conducive to the reduction reaction.The metallization rate and strength of the pellet after reduction are at a high level.