Internal Structure Evolution Mechanism Of Unclassified Tailings Mortar After The Floc Net Structure Strengthened By APAM

In recent years,China has gradually accelerated the pace of construction of green mines for mining enterprises,promoting the harmonious development of mining development and natural ecological environment.As a key technology for green mine construction,full tailings filling has the advantages of simple process,cost reduction and environmental protection,which can effectively solve the ecological safety problems such as tailings accumulation and stability of mining area.However,the actual unclassified tailings mortar used for filling in mines is often lower than the design concentration,and the flocculants remaining in the thickening process have a great impact on the internal structure of the mortar,and the pipeline transport characteristics of unclassified tailings mortar are very different from those before,and little relevant research has been conducted.In this paper,based on indoor tests,theoretical analysis and other research methods,particle size tests,scanning electron microscopy（SEM）tests and nuclear magnetic resonance（NMR）tests were conducted on unclassified tailings mortar with and without the addition of anionic polyacrylamide（APAM）,and computer image processing techniques and fractal theory were used to analyze and explore the mechanism of the effect of APAM enhanced flocculation network structure on the internal structure of the mortar.The effect of APAM on the macroscopic rheological properties of the mortar was also revealed by constant shear rheology tests,and the main research contents and results of this paper are as follows:（1）Based on the results of physicochemical properties testing of unclassified tailings of a copper mine,the best way to settle and concentrate the unclassified tailings mortar was obtained by conducting unclassified tailings flocculation and sedimentation test.The indoor flocculation and sedimentation test results show that APAM with a relative molecular mass of1×10⁷has the best sedimentation effect as flocculant,and the concentration of APAM is 1‰and the unit consumption is 20g/t in the quantitative test.（2）The results of particle size test showed that after adding APAM,the difference of coarse particle content in each stratum decreased under the same resting time,and the coarse particle content in the bottom stratum was smaller than that in the middle and lower stratum（stratum 10 and stratum 15）in both 66%concentration mortar and 76%concentration mortar,and the coarse particle content in stratum 15 of 66%concentration mortar was 60.89%and61.87%respectively after 30 and 40 min of resting,while the coarse particle content in stratum 15 of 76%concentration mortar was 60.89%and 61.87%respectively.61.87%,while the coarse particle content of the middle layer of 76%concentration mortar increased linearly with the resting time,and the coarse particle content of this stratum was the largest during the whole resting process,especially at 30min and 40min,the coarse particle content was 51.32%and 51.78%respectively,which was much larger than other strata.The reinforced flocculent network structure formed by the bridging effect interferes with the settling of coarse tailing sand more easily,and the coarse particles are captured and dispersed in the mortar system by these network structures during the settling process,resulting in a more uniform distribution of coarse particles in the vertical direction.（3）According to the SEM test results,when APAM is not added,the tailings and cement particles are disordered in the mortar,and some of the fine particles of tailings accumulate to form flocs through the action of compressed double electric layer（self-flocculation）.At this time,there is no stable structure between the particles,there are a great quantity of pores between the particles,and the fine particles are distributed around the coarse particles.After the addition of APAM,the active groups on the polymer chain are adsorbed on the surface of the particles and form a flocculent network structure with strong structural stability through mutual crossover and lap,which enhances the cohesive effect of the particles and reduces the inter-particle pores inside the mortar.In addition,the development degree of the mortar without and with APAM was not the same at different resting times,with obvious fractal characteristics,and the fractal dimension and structure coefficient of the mortar increased after the addition of APAM,and the structural evolution characteristics of the mortar were more obvious after the addition of APAM in 76%concentration mortar.With the increase of resting time,the increase of structure coefficients of the two mortars decreased,but the structure of floc network formed by self-flocculation was still lower than that of the APAM-enhanced floc network.（4）According to the NMR test results,the three peaks of T₂spectrum from left to right corresponded to the NMR signals of hydrogen nuclei in adsorbed water,flocculated water and free water in the mortar in turn.With the increase of the resting time from 0 min to 40 min,the pore distribution of the mortar was more uniform at each layer of the mortar after the addition of APAM,and the relaxation time of free water showed a significant left shift,while the relaxation time of adsorbed water and flocculated water changed less.As the shear rate increased from 10s^-1to 50s^-1,the peak area of（1）decreased from 7.455 and 7.022 to 6.848 and6.490 in the mortar without and with APAM,respectively,with a decrease of 5.8%and 7.6%,respectively;the peak area of（2）decreased by 51.3%and 40.1%,respectively;and the peak area of（3）decreased by 94.4%and 100.0%,respectively.APAM reduced the activity of water,free water migrated rapidly to more stable water,and some free water in the mortar was gradually converted to flocculated water.The resting time and shear strength can promote the conversion of free water and floc water inside the mortar,while APAM further improves the migration of adsorbed water and free water in the mortar.（5）The results of the rheological parameters under constant shear showed that the mortar without and with APAM had obvious shear thinning characteristics.With the increase of shear time,the apparent viscosity and shear stress of the two groups of mortars gradually decreased and reached the equilibrium value at a certain time,and the apparent viscosity and shear stress of the mortar with APAM were larger than those of the mortar without APAM,which changed the properties of the mortar,the apparent viscosity of the mortar increased and the Reynolds number decreased,the fluid flow developed to laminar flow,and the stability of the mortar increased.With the increase of shear rate,the relative changes of apparent viscosity and shear stress of unadded and added APAM mortar gradually decrease,and the influence of APAM polymer on the rheological properties of mortar under the effect of high shear rate decreases.In the actual filling,the mixing rate of the residual APAM unclassified tailings mortar can be increased to fully destroy the flocculent network structure and thus reduce the influence of viscosity,and reduce the energy loss of the mortar in the conveying process.