Research Of The Wastewater From The Wet Reclaiming Sodium Silicate Used Sand By Diatoms Disposing

Among all kinds of mould sand, the sodium silicate sand is one of the mostpossible mould sand that can realize green casting. But the key point to realize greencasting based on sodium silicate sand is achieving reclamation of sodium silicate usedsand with no pollution. As we all know that the wet reclaiming method is better than otherreclaiming methods because of its high removing rate of the remnant film and highreusing rate, but high cost of the alkaline wastewater treatment produced by wetreclaiming and its complex system hinder the popularization and application of wetreclaiming of sodium silicate used sand. Therefore, the research of wastewater processingand recycling in wet reclamation of sodium silicate used sand is one of the crucialtechnologies that can realize complete reclamation and reuse of sodium silicate used sand.A new process which used diatom to treat the wastewater produced during the wetreclamation process of sodium silicate used sand was firstly proposed in this paper. Bycomparing three diatom species of Nitzschia palea, Cyclotella meneghiniana and Melosiravarians, the growth of three diatoms and treatment effect of the wastewater were studied indifferent conditions. The result indicates that Nitzschia palea can rapidly adapt to thealkaline wastewater environment, which comes from wet reclaiming of sodium silicateused sand. And the wastewater treatment effect is good, during which Nitzschia palea wasselected as the optimum diatom to treat the wastewater. After7days treatment, theconcentration of Na+decreased from1.49g/L to0.86g/L and Na+removal rate is40.8%,and also the concentration of SiO32-decreased from0.51g/L to0.26g/L and SiO32-removalrate is48.1%, the pH value of wastewater decreased from11to9, when Nitzschia paleawas in the condition of temperature25℃, irradiance5000lux, illumination time14h/d, Nconcentration80mg/L, N: P14:1. Further study found that the efficiency of the wastewatertreatment will be relatively reduced when the diatom initial addition amount is largerbecause of the constraint of the diatom growth space. At the same time, the longer time thewastewater is treated by diatoms, the relatively lower treatment efficiency it is.The wastewater recycling is also studied. The results show that when the wastewaterafter treatment in accordance with the ratio1:2of sand and water scrubs the next batch of sodium silicate used sand, de-skinning ratio is up to92%, but when the tap water with thesame ratio is used to scrub used sand，de-skinning rate is85%. Meanwhile, compared thenew sand with the other two kinds of sand by different wet reclaiming, the tap water andthe wastewater which treated by diatom, the results indicated that the1h,2h,4h,24hstorage strengths of new sand are significantly higher than that of the other two reclaimedsand. As for the comparison of two kinds of wet reclamation sand,1h storage strength ofthe sand reclaimed by tap water is slightly higher than that of the sand reclaimed by thewastewater treated by diatom. However,2h,4h,24h storage strengths are same. After4hours, these three sand storage strengths have a little change. Therefore, the wastewatertreated by diatom can be used to scrub the next batch of sodium silicate used sand andrealize the recycling of wastewater.