Study On Preparation Of Sintered Bricks From Iron Tailings And Its Leaching Characteristics

In recent years,China's iron tailings pile stock increased year by year.It is urgent to develop effective technical route to improve the comprehensive utilization rate of iron tailings because of the large stockpile,low comprehensive utilization rate and environmental problems caused by the stockpiling process.The preparation of sintering brick is a new way of resource utilization of iron tailings.On the one hand,it can solve the environmental problems caused by iron tailings stockpiling at the source.On the other hand,it can also make resource utilization of solid waste and give the application value of iron tailings again.However,iron tailings contain a variety of heavy metals,and there is a risk of heavy metal leaching after the preparation of sintering bricks.Therefore,it is necessary to study the heavy metal leaching of iron tailings sintering bricks,so as to provide a basis for the safety of iron tailings resource utilization.Based on the physical and chemical properties of iron tailings from Dabaoshan,Guangdong Province,the main composition and phase composition of iron tailings are analyzed.The sintering bricks were prepared by adding fly ash,waste glass and other auxiliary materials.The effects of different sintering temperature and ratio on the properties of the sintering bricks were studied,and the best preparation process conditions of the sintering bricks were obtained.Taking sintering temperature as a variable,the change of sintering bricks in the sintering process was explored to illustrate the curing process.In both acid and nitric acid and acetic acid leaching method,leaching experiment was carried out on the sintered brick,to explore the different p H,reaction time,solid-liquid ratio on the leaching of heavy metals in the clinker,also on sintered brick before and after the leaching of heavy metal content,microstructure and morphological analysis of heavy metals,to illustrate sintered brick in the leaching of heavy metals before and after the change.The main research results are as follows:The main mineral forms of iron tailings are hematite,quartz and kaolinite,among which kaolinite is a clay mineral and is an ideal material for the preparation of sintering bricks.However,the content of heavy metals in iron tailings is relatively high,in which the total contents of Cu,Pb,Zn,Cr and Cd are 2 814.92,1 992.12,1 712.33,63.26 and 10.84 mg·kg^-1,respectively.Despite the fact that iron tailings contain similar compositions compared with clay,the raw material for traditional sintered bricks,the technical route used to prepare sintered bricks is feasible.However,iron tailings contain high amount of heavy metals,so it is necessary to explore the leaching situation of iron tailings sintering bricks.Solid wastes such as fly ash and waste glass were used as auxiliary materials to prepare sintered bricks with iron tailings.Under the optimal sintering temperature of 1 100?and iron tailings:fly ash:glass ratio of 6:2:2,the compressive strength and water absorption of the sintered bricks are 124 MPa and 4.6%respectively.The leaching concentration of Cu,Pb and Zn was low.When the sintering temperature increases from 900?to 1 200?,the proportion of Cu,Pb and Zn residues increases,the pore volume decreases from 0.019 cm³·g^-1 to 0.010cm³·g^-1,and the average pore diameter decreases from 22.1 nm to 9.3 nm.The phase analysis showed that the mullite phase was formed by the reaction between kaolinite phase and quartz in the sintering process,which promoted the formation of sintering brick.Under the conditions of strong acid and alkali pH of 1 and 13,the leaching amount of Pb and Zn is high,while the leaching amount of Cu is high only under acidic conditions,and the leaching amount of heavy metals is low under p H of 7-11,and the leaching risk is the least.When the solid-liquid ratio is greater than 1:20,the extraction effect of acetic acid on Cu,Pb and Zn is greater than that of sulfuric acid and nitric acid method due to ionization.Before the reaction time of 20 h,the leaching quantities of Cu,Pb and Zn all increase with the increase of time,but after 20 h,the leaching quantities of Cu,Pb and Zn remain stable.The leaching environment can promote the migration or transformation of the weak acid extraction states of Cu,Pb and Zn.Among the three kinds of heavy metals,Cu has the most unstable form and is easy to be released under acidic conditions.SEM analysis also shows that the two leaching methods erode the skeleton structure of the sintered bricks to different degrees,so a large number of small pore size structures appear on the surface of the sintered bricks.In the short experiment period of 0?30 h,under different p H,solid-liquid ratio and reaction time conditions,the leaching quantities of Cu,Pb and Zn of iron tailings sintering brick are all low,indicating that the leaching risk is small.