Research status and development of extraction process of zinc-bearing dust from ironmaking and steelmaking—a critical review

Almost 29.57–38.46 million tons of zinc-bearing dust were produced in Chinese iron and steel enterprises annually.The recovery of Zn and other metals in zinc-bearing dust from ironmaking and steelmaking could improve economic efficiency.However,zinc-bearing dust was classified as hazardous waste,and the volatile metals(like Zn,Na,Pb,etc.)in zinc-bearing dust limited the direct reusing in a blast furnace.Therefore,the formation process,fundamental characteristics,and current extraction process of Zn from zinc-bearing dust,associated with thermodynamics and kinetics of the pyrometallurgical process,hydrometallurgical process,and pyro-hydrometallurgical process,were analyzed.It is indicated that industrialized pyrometallurgical processes are undergoing high energy consumption and pollution such as rotary kiln and rotary hearth furnace process.The vacuum carbothermal reduction process can realize low carbon emission and no waste produced in the process.The hydrometallurgical leaching processes in strong acid,strong alkali,and ammonium solutions result in serious liquid pollution and equipment corrosion.The pyrometallurgical process involves complex kinetics and lacks kinetic research on semi-industrialization and industrialization.Water-soluble components in zinc-bearing dust can be removed by water leaching.The kinetics of the strong acid leaching is mainly controlled by the leaching kinetics of Fe_(2)O_(3) and ZnFe_(2)O_(4),while the alkali leaching and weak acid leaching are controlled by the kinetics of ZnO leaching.Zn in the zincbearing dust can be extracted by a low-temperature sodium roasting–weak acid leaching process that reduces equipment corrosion and environmental pollution.

A high-efficiency separation process of Fe and Zn from zinc-bearing dust by direct reduction

It is urgent to dispose of zinc-bearing dust from steel plants,and direct reduction process is an effective method to remove hazardous metals and recycle iron from the dust.The reduction behavior of carbon-containing pellets which were made from three kinds of zinc-bearing dust was investigated.When the pellets were reduced at 1200℃ for 50 min,the reduced pellets with cold compressive strength of 1164 N pellet−1 and Zn content<0.1 wt.%could be directly used as burden for improving the blast furnace operation without further agglomeration.The results of isothermal kinetic study showed that the iron oxide reduction rate was controlled by the chemical reactions.The strengthening mechanism of reduced pellets and iron oxide reduction mechanism was investigated by thermodynamic calculation besides X-ray diffraction,scanning electron microscopy combined with energy dispersive spectrometry,and optical microscopy analyses.It was found that higher temperatures are required for the reduction of spinel phase(zinc ferrite)and olivine phase(hedenbergite).The generation and growth of metallic iron bridges could significantly increase the compressive strength of reduced pellets.The iron oxide reduction in the carbon-containing pellets followed the uniform internal reduction model and possessed a high apparent reaction rate,which can improve energy utilization rate and production efficiency.

Characteristics of the reduction behavior of zinc ferrite and ammonia leaching after roasting

A novel method for recovering zinc from zinc ferrite by reduction roasting–ammonia leaching was studied in this paper. The reduction thermodynamic of zinc ferrite by CO was analyzed. The effects of roasting parameters on the phase transformation and conversion rate of zinc ferrite, and the leaching behavior of zinc from the reductive roasted samples by ammonia leaching, were experimentally investigated. The mineralogical phase compositions and chemical compositions of the samples were characterized by X-ray diffraction and chemical titration methods, respectively. The results showed that most of the zinc ferrite was transformed to zinc oxide and magnetite after weak reduction roasting. 86.43% of the zinc ferrite was transformed to zinc oxide under the optimum conditions: CO partial pressure of 25%, roasting temperature of 750°C, and roasting duration of 45 min. Finally, under the optimal leaching conditions, 78.12% of zinc was leached into the solution from the roasted zinc ferrite while all iron-bearing materials were kept in the leaching residue. The leaching conditions are listed as follows: leaching duration of 90 min,ammonia solution with 6 mol/L concentration, leaching temperature of 50°C, solid-to-liquid ratio of 40 g/L, and stirring speed of 200 r/min.

Integration of preparation of K,Na-embedded activated carbon and reduction of Zn-bearing dusts

Large amounts of solid wastes and flue gases are generated in iron and steel production process,probably leading to serious environmental pollution without duly handle.An innovative and green process of simultaneous reduction of zinc-bearing dusts and activation of low-rank coal was developed and its mechanism was clarified in this paper.Under the optimal conditions,the reduced zinc-bearing dusts containing low harmful elements(0.02%Zn,0.015%K and 0.03%Na)could be made as high-quality burden for blast furnace while the low-rank coal was transferred into K,Na-embedded activated carbon,which can be used as effective adsorbent for purification of SO_(2) and NO-containing flue gases.The solid wastes were successfully utilized to treat the flue gases through the process.The synergetic activation and reduction mechanism in the process was revealed.The coupling effect between reduction reactions of metal oxides in the dusts and activation reaction of carbon in the coal promoted the simultaneous reduction and activation process.In the meanwhile,part of the potassium and sodium from the zinc-bearing dusts could be adsorbed by the activated carbon and played a catalytic role in the activation process.

Removal Mechanism of Zn,Pb and Alkalis from Metallurgical Dusts in Direct Reduction Process

The high-temperature tube furnace was applied to simulate the rotary hearth furnace （RHF） for the direct reduction of zinc-bearing dusts from steel plants. The removal mechanism of Zn, Pb and alkalis from cold bonded briquettes made by mixing metallurgical wastes, such as dust from bag house filter, OG sludge, fine converter ash and dust from the third electric field precipitator of the sinter strand, in various proportions was investigated. More than 70% of metallization rate, more than 95% of zinc removal rate, 80% of lead removal, as well as more than 80M of K and Na removal rates were achieved for the briquettes kept at 1473-1603 K for 15 min during the direct reduction process respectively. The soot generated in the direct reduction process was studied by chromatography, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results suggested that the main phases of the soot were ZnO, KC1, NaC1 and 4ZnO · ZnC12 · 5H20. Furthermore, the content of Zn reached 64.2 %, which could be used as secondary resources for zinc making. It was concluded that KC1 and NaC1 in secondary dust resulted from the volatilization from the briquettes, whilst ZnO and PbO were produced by the oxidation of Zn or lead vapour from briquettes by direct reduction.