Research On New Technology Of Wet Reclamation Of Waste Sodium Silicate Sands With Low Water Consumption

Sodium silicate sand has many advantages such as good fire resistance,high strength,low cost and environmental friendliness,and is widely used in countries all over the world.Futher improvements in the process and materials of sodium silicate sand are considered to be most likely to achieve green casting.The main drawback of sodium silicate sand is still the difficulty in reclamation of waste sodium silicate sands.Many researches and practices have shown that wet reclamation is the most effective method of reclaiming the waste sodium silicate sands.However,the current wet reclamation process consumes a large amount of water,and a large amount of alkaline sewage is discharged,causing secondary pollutio n.Therefore,reducing the water consumption of wet reclamation and solving the problem of reusing and disposal of wet reclamation sewage are the keys to the widespread approval and adoption of wet reclamation.In this paper,aiming at a low water consumption wet reclamation method of the waste sodium silicate sands,several new methods of reclaiming the waste sodium silicate sands with low water consumption were proposed and studied.On this basis,a method of recycling water glass from wet reclamation sewage was studied.The methods of reclaiming unwieldy waste sodium silicate sand hardened with carbon dioxide were studied at last.The main contents in this paper are summarized as follows:?1?A method of ultrasound-assisted wet reclamation of the waste sodium silicate sands was proposed.The parameters of ultrasound-assisted wet reclamation were investigated.The properties of the waste sands and reclaimed sands were compared.The mechanism of ultrasonic-assisted wet reclamation was analyzed.The results show that improving the ultrasonic power,increasing the water comsumption,prolonging the ultrasonic treatment time,and increasing the number of reclamation times can increase the Na₂O removal rate.After one-time ultrasonic-assisted wet reclamation,a little sodium silicate remains on the surfaces of the reclaimed sand grains,and the reclaimed sand has a high bonding strength and can be directly reused.The thermal,chemical and mechanical effects of the ultrasound cause the sodium silicate on the surfaces of the sand grains to enter the water.The sodium silica te enters the water by dissolving and breaking into particles.?2?A new method of the integration of wet reclamation and dehydration of the waste sands by drum was proposed,and an experimental device based on the method was manufactured.The parameters of wet reclamation by drum were investigated,and the properties of the reclaimed sand were analyzed.The results show that increasing the rotary speed,and prolonging the dehydration time can reduce the water content of dehydrated reclaimed sand,and the Na₂O removal rate can be increased by choosing the appropriate rotary speed,increasing the water consumption,prolonging the treatment time of drum,and increasing the number of reclamation times.A little residual sodium silicate is on the protruded surfaces of the reclaimed sand grains,and much residual sodium silicate is on the depressed surfaces of the reclaimed sand grains.After one-time wet reclamation by the drum,the reclaimed sand has a high bonding strength and can be directly reused.?3?Based on the analysis and experimental study on the water consumption control mechanism of wet reclamation,a new method of extremely low water consumption wet reclamation with“rinse-dehydration”was proposed and investigated.The results show that the“rinse-dehydration”treatment of the dehydrated reclaimed sand can remove the Na₂O in the residual sewage from reclaimed sand with a small amount of water,and achieve a high Na₂O removal rate under the condition of low water consumption.On the basis of“rinse-dehydration”,the sewage can be reused after being filtered,which can further reduce the water consumption without significantly reducing the Na₂O removal rate,and achieve extremely low water consumption wet reclamation.?4?A method of recycling water glass from high concentration wet reclamation sewage of the waste sodium silicate sands was proposed and studied.The results show that the suspended matter in the sewage can be removed by filtration,and the organic matter in the sewage can be partial removed by ozone oxidation.The sewage without suspended matter and organic matter can be converted into lye by a causticizing process.The silica in the filter residue?suspended matter?can dissolve in the lye and form water glass,and the bonding strength of the recycled water glass is close to that of commercial water glass with the same modulus and density.?5?The unwieldy waste sodium silicate sand hardened with carbon dioxide and repeated use by a certain enterprise is used as the object,and several reclamation methods were compared to find out a preferably method of reclaiming the unwieldy waste sodium silicate sand.The results show that the ultrasound-assisted wet reclamation and drum wet reclamation can achieve high Na₂O removal rates,but the reclaimed sands have low bonding strengths and cannot be directly reused.Alkali-cooking reclamation,“ultrasound+acid leaching”reclamaition,and“drum+acid leaching”reclamation can achieve Na₂O removal rates higher than 90%,and the reclaimed sands have high bonding strengths and can be directly used to replace new sand.The new wet reclamation methods of waste sodium silicate sands proposed in this paper aim at environmental protection targets such as low water consumption,less sewage discharged,and recycling water glass.These achievements have important theoretical and practical significances for promoting the development and application of new green casting technologies for the sodium silicate sand.