Study On The Technology Of Pre-Paring Mechanical Sand Barrier From Waste Salty Tailings

Land desertification has become a major national ecological and environmental problem that seriously restricts the development of national economy.At present,the sand barrier materials used for wind prevention and sand fixation in China are clay,firewood,pebble,gravel,nylon and plastic mesh,but they can not be widely used due to the problems of easy aging,low efficiency,high cost and residual impact on the environment.The cost and environmental compatibility of sand fixing materials are the key factors.It is urgent to find low-cost and environment-friendly sand barrier materials.Iron tailings are solid wastes with low content of useful components produced in mine beneficiation.The massive stockpiling of iron tailings cause great environmental pollution and serious waste of land resources.The tailings in northern Hebei are piled up seriously.Fine and micro fine iron tailings are easy to form dust storms in stormy weather,and the land near the wind blown sand area of the traffic trunk line is seriously salinized.It is very easy to form chlorine salt iron tailings in the wind erosion environment,which poses great harm to the operation safety of the traffic trunk line in the tailings stacking section and its adjacent areas and causes great pollution to the environment.Aiming at the current situation of wind sand disaster caused by iron tailings on regional traffic trunk lines in northern Hebei,combined with the unique sand source of salty tailings in northern Hebei,cement curing method and aggregate grading principle,this study designed and used salty iron tailings according to local conditions,carried out curing tests on salty iron tailings with different particle sizes,and carried out technical research on the curing mechanism of solidified iron tailings to prepare wind proof and sand fixation curing specimens.Focusing on the comprehensive utilization of iron tailings,focusing on the change law of dry wet cycle,freeze-thaw cycle and weathering resistance of iron tailings as sand barrier material and solidified specimens,this thesis discusses the effects of different factors such as temperature,moisture,weathering and UV erosion conditions.By using unconfined compressive strength test,combined with fine and micro test methods such as USB,SEM,XRD and nitrogen adsorption,the key parameters and conditions of sand fixation specimens are determined and optimized scientifically.The solidification mechanism of sand fixation specimens is analyzed from the macro and micro point of view,and the key technologies of iron tailings sand fixation specimens are obtained.The conclusions are as follows:(1)The orthogonal test shows that the primary and secondary order of influencing factors on the compressive strength of solidified specimens is: tailings particle size > cement > slag > calcium oxide > ionic curing agent > water.The optimal ratio of chloride tailings solidified specimens is tailings: cement: ionic curing agent: slag: calcium oxide: water = 1:0.12:0.022:0.14:0.08:0.10,and the optimal particle size of iron tailings is 0.075<d<0.3mm.After the ratio is improved,the overall strength can reach more than 11.0Mpa,which Fully meets the requirements of wind prevention and sand fixation.(2)The microstructure analysis of the cured specimen shows that the internal structure of the specimen is compact and the porosity is low.A large number of fibrous,flaky and needle rod hydration products and continuous folded and cluster C-S-H gels are generated by the compound mixing of cement,slag and other curing agents.The reduction of interface pores,the improvement of the compactness of hydration products,the increase of the number of hydration products of curing agents and the reduction of the volume of voids are the main factors for the strength enhancement of cured specimens.(3)The compressive strength of cured specimens decreased with the increase of dry wet cycles;With the increase of freeze-thaw cycles,the strength increased slightly at first and then decreased gradually;With the increase of weathering time,the strength of the specimen with sodium sulfate was decreased increased decreased.The durability test shows that sodium chloride can alleviate the influence of sodium sulfate on the strength of the specimen,adding a small amount of sodium chloride has a relatively good effect on the strength of the solidified specimen,and adding salt can significantly enhance the wind erosion resistance of the tailings specimen.(4)Different grading iron tailings sand particles have fractal properties.With the increase of fractal dimension D,the grading gradually transits to dense grading.The finer the iron tailings sand particles,the better the grading.The pore fractal dimension D values of solidified specimens containing 0% salt,1% sodium chloride,1% sodium sulfate,0.5% sodium chloride +0.5% sodium sulfate are 2.709,2.596,2.413 and2.592 respectively,which are close to 3,indicating that the pore density of solidified tailings with different salts is very high within a certain scale range,and the macroscopic performance is very high compressive strength.(5)The pore diameter of tailings solidified specimens with different salts is basically distributed between 2-50 nm,and the pore mainly consists of medium and large pores,with a small number of small pores.For the cured specimens of sodium sulfate tailings after dry wet and freeze-thaw cycles,the pore size is basically distributed between 2-100 nm,the large pore size increases,the specific surface area gradually decreases,the fractal dimension D is between 2.35-2.60,and the compressive strength decreases.