Preparation And Performance Study Of Phosphate Tailings-based Foam Packing

Green and safety are the eternal themes of mine construction.The instability of the mined-out area,the land occupied by the tailings stacking and the deterioration of the ecological environment are the important factors restricting the development of the mine.In recent years,the use of tailings to fill mined-out areas has been widely concerned and gradually popularized.Foam filling has the advantages of high seed setting rate,high support top bonding rate.The research on the preparation and performance of phosphate tailings-based foam filling system is of great significance to make full use of phosphorus tailings and protect the green,safe and sustainable mine.Based on the analysis of the physicochemical properties of foaming filling materials,phosphorus tailings based foaming filling materials and aggregate and phosphorus tailings foaming filling materials were prepared through conditional tests.Their properties were studied in common maintenance environment and rich water environment respectively,and the optimal ratio of filling materials was determined.At the same time,combined with the actual situation of mine filling,considering the filling strength and the dissolution of harmful ions,this paper puts forward the "layered filling method" of using aggregate and phosphorus tailings foam filling in the lower layer of goaf and phosphorus tailings foam filling in the upper layer,which provides an effective method to improve the safety and environmental protection of phosphorus tailings foam filling.The main conclusions are as follows:(1)The results of single factor test show that with the increase of cement content,the viscosity of foam filling slurry increases,the fluidity decreases,the resistance of bubble expansion increases,the porosity of foam filling body decreases and the pore diameter decreases.The glass beads in fly ash can fill the pore space,enhance the stability of bubbles and improve the compressive strength of foamed filling body.When the water cement ratio is small,the formation of bubbles is blocked and the cementitious material is not evenly dispersed.When the water cement ratio is large,the slurry is diluted,and the bubbles are easy to connect and merge,increasing the content of large pore.With the increase of the amount of foaming agent,the pore size increases and the compressive strength decreases.Superplasticizer can not only disperse the cementitious substances effectively,but also reduce the possibility of bubble connection and merger.when content of the cement and fly ash are 30% and 20%,the water-cement ratio is 0.42,the foaming agent and the water-reducing agent are2.5% and 0.3%respectively,the slump expansion of the foam filling slurry is 208 mm,the compressive strength and the volume expansion rate of the foam filler which is cured for 28 d are2.7Mpa and 28.53% accordingly,meanwhile,the average pore diameter inside the filler body is 0.26 mm,the pore roundness value is 1.04 and the phosphate tailings foam filler has high performance.(2)The 28 d compressive strength of the aggregate stirred in phosphate tailing foam filler after mixing 40% of the full-grain aggregates is 3.4MPa.Aggregate can block the penetration of water molecules to a certain extent,and slow down the strength damage of the foamed test block and the dissolution rate of harmful ions in the waterrich environment.When the filling technology is applied to engineering practice,aggregate stirred in phosphate tailing foam filler can be used to fill the lower layer and phosphate tailing foam filler used to fill the upper layer of the mined-out area.This is good for improving the safety of filling and environmental protection effectively.