Research And Development Of Iron Tailing Based Filling Material And Its Properties

A large number of mined out areas have been formed in some mines,surrounding areas and karst areas in China,which has become an important problem restricting the safe development of mines and the urbanization development of the upper part of the mined out areas,and has brought great hidden dangers of safe production,which need to be solved reasonably.Filling method is one of the most effective ways to control goaf,filling material is the core to ensure the quality of filling engineering.But,at present,cement and its substitutes are the common filling materials,gravel,sand,tailings,etc.are used as aggregate,there are some problems such as high filling cost,serious environmental pollution and low utilization ratio of tailings.At the same time,with the increasing number of iron tailings,there are more and more environmental safety problems caused by iron tailings stacking,which are widely concerned by the community.Therefore,the filling treatment of underground engineering and the high added value utilization of iron tailings have become the key scientific problems to be solved.In this paper,according to the needs of filling engineering and the current situation of low added value utilization of iron tailings,through the combination of investigation and research,indoor experiment and numerical analysis,the iron tailings based filling material is developed,and its physical and mechanical properties and working performance are studied by experimental analysis and numerical simulation.The main research contents and achievements are as follows:(1)In view of the low activity of the original iron tailings,which can not be used as cementitious materials directly,the active excitation technology of the iron tailings was studied by means of the combination of mechanical grinding and chemical excitation,and the feasibility of the activated iron tailings as cementitious materials for filling was analyzed.After mechanical grinding for 30 min and passing 270 mesh square hole sieve,the activity index of iron tailings increased to 68.1%,the activation mechanism of iron tailings was analyzed by XRD and SEM-EDS(2)In order to determine the system composition of cementitious materials for filling,the test method for the activity of industrial waste residue used as cement admixture(GB/T12957-2005)is used for reference,and the compatibility test of solid waste was carried out in the proportion of iron tailings:slag(fly ash,coal gangue)=7:3,according to the compressive strength,the effect of iron tailings slag binary system was the best.When the content of sodium hydroxide was 4%,the compressive strength of the stone can reach 6.15 MPa in 28d.It was determined that the iron tailings slag binary system was the main component of the cementitious material of iron tailings for filling.The hydration products were analyzed by XRD and SEM-EDS.(3)Based on the theory of synergetic and complementary utilization,the paper puts forward that the cementitious material was the ternary system of iron tailings slag clinker.Through the ratio experiment,the influence of the type and amount of alkali activator,the amount of clinker and the amount of slag on the compressive strength of the cementitious material was studied.The optimal ratio of iron tailings based cementitious material was:iron tailings 64%,slag 30%,clinker 6%,alkali activator Sodium hydroxide,2%(4)The filling material of iron tailing base was prepared by using the cementitious material of iron tailing base as the cementitious material and the undisturbed iron tailing sand as the aggregate.The effects of mass concentration and mortar ratio on physical and mechanical properties(bleeding rate,stone rate,volume stability and compressive strength)and working properties(fluidity and rheology)of materials were studied.The mass concentration and the ratio of cement to sand can be adjusted dynamically according to the needs of filling engineering,which can not only meet the compressive strength of stone body and the fluidity of slurry,but also reduce the cost of filling and improve the applicability of filling engineering.The experimental results showed that when the mass concentration of slurry was 70%and the ratio of cement to sand was 1:4,the bleeding rate of filling slurry was 4.66%,the fluidity was 188 mm,and the 28 day compressive strength of stone body was 2.03 MPa,which meets the requirements of most filling projects.With the extension of curing time,the dry shrinkage rate of stone body gradually increased,and the change of stone body volume dry shrinkage was the most significant after curing for 7 days(5)In this paper,FLAC 3D was used to simulate the deformation law and the stability of surrounding rock after filling,which providied a scientific basis for the application of filling material in goaf.