Preparation Of Magnesium Oxalate Chemical Bonding Material And Study On Its Solidification Of Heavy Metal Zinc

Magnesia-phosphate chemical bonding material is composed of magnesium oxide soluble phosphate and addictive in certain ratio and is able to produce phosphate hydrates as binder by the neutralization reaction between acid and base.it has excellent properties of cement and ceramics.it can be used in many fields,such as road rapid repair,hazardous waste solidification,biological bone bonding material and so on.But magnesium phosphate chemical bonding materials contain more phosphorus,which easily lead to eutrophication.In this paper,magnesium oxalate chemical bonding materials?M-CBOM?were prepared by using magnesium oxide and oxalic acid/acid oxalate,their heat resistance and water resistance were studied,then the M-CBOM were modified by using industrial waste residues.they were used as a matrix material to solidify zinc nitrate.The results and conclusions of the study are as follows:?1?The factors influenced on the properties of the M-CBOM were systematically studied,including the acid components,the acid-base ratio?C/M?,the calcination temperature of magnesium oxide,the content of borax and the water-glue ratio.The better scheme was obtained,it was that:the acid component was KHC₂O₄,the C/M was 1:3,the calcination temperature of magnesium oxide was 1300?,the content of borax was 4%,the water-glue ratio was 18%.The seeting time of the materials was9min,The compressive strength of the materials by natural curing 1d and 28d were16.61MPa and 32.65MPa.XRD?FT-IR?TG showed that:the system produced an infinite chain of Mg C₂O₄·2H₂O and Mg C₂O₄ as binder through a reaction of acid and base.they were arranged closely and they connected the unreacted Mg O togher to form a dense and high intensity magnesium oxalate chemical bonding materials.?2?By examining the heat resistance of M-CBOM,The results are as follows:when the temperature was below 100?.the surface color and volume of the samples changed small but the compressive strength changed greatly when the samples treated at different temperature.The amount of oxalate binder,the density and the compressive strength of the samples increased with the increasing of temperature,the compressive strength can reached as high as 34.80MPa.When the temperature was between 150?and 250?,Mg C₂O₄·2H₂O dehydrated and formed into Mg C₂O₄,but it had little influence on the morphology of the M-CBOC,the loss of compressive strength of the samples which treated at 250?was only 17%.When the temperature was between 300?and 600?,the Mg C₂O₄ decomposed into Mg O and Mg CO₃,There were micropores in the materials,the structure of the materials had collapsed,the compressive strength of the samples decreased significantly.the loss of compressive strength of the samples was 88%when the temperature reached 600?.?3?By examining the water resistance of M-CBOM,The results are as follows:If the samples were soaked in water for a long time,they would be eroded seriously Mg C₂O₄·2H₂O,Mg C₂O₄ and unreacted Mg O could dissolve and crystal in surface of samples,a lot of micropores were left in the materials so that the structure of the materials was loose,the compressive strength and the softening coefficient decreased.The softening coefficient of the samples soaked for 1d was 0.81,soaked for 28d was0.39.The mass loss of samples soaked for 28d was 5.83%.?4?Fly ash,slag and sand were used to modify the M-CBOM,the better ratio of the modifying materials was obtained by the single factor and double factor experiments.It was that:The fly ash 15%,the sand 25%.The setting time of the materials prepared by this scheme was extended to 20min,the compressive strength of the materials by natural curing for 28d was 33.99MPa,and the compressive strength of the materials curing at 100 C for 48h was as high as 39.52MPa.XRD and SEM showed that:Taking sand as condensation nodule,Mg C₂O₄ 2H₂O and Mg C₂O₄as skeleton,unreacted Mg O and fly ash as filler,Mg Al₂O₄·7.9H₂O and Mg Al₄Si₅O₁₈bonding them togerther formed a MM-CBOC which had a more compact structure.?5?By examining the weather resistance of MM-CBOM,the results are as follows:The heat resistance and water resistance of MM-CBOM were improved.After modified,the compressive strength of samples improved at different temperatures,especially in the higher temperature.the strength loss of the modified samples treated at 600?was increased to 66.5%.The softening coefficient of the samples soaked for 1d increased from 0.81 to 0.85,and the softening coefficient of the samples soaked for 28d increased from 0.39 to 0.44.?6?By examining the zinc nitrate Solidification by MM-CBOM,the results are as follows:MM-CBOC had good Solidification effect on zinc nitrate,The maximum solid capacity could reach to 15%.XRD and SEM showed that,The mechanism of zinc nitrate solidification by MM-CBOM was that,the formation of Zn C₂O₄·2H₂O by the reaction of Zn and Potassium hydrogen oxalate,followed by physical inclusion using MM-CBOM to achieve the purpose of heavy metal?Zn?solidification.