Removal Of Heavy Metals Cd(?) And Pb(?) From Apple Juice With Porous Stainless Steel Supported Iron Oxides Membranes

In recent years,with the rapid development of economy and advancement of industry and agriculture and the acceleration of the urbanization process in our country,atmospheric contamination,sewage sludge and excessive use of fertilizers&pesticides have attracted increasing attention and are among the causes of contamination of water,soil and raw food stuffs.Research shows that the major heavy metal ions in apple juice including arsenic?As?,lead?Pb?,cadmium?Cd?and chromium?Cr?can cause irreversible harm to human body.However,there are no effective methods availabe for the industrial removal of the heavy metal ions to effectively control the situation.The development of economic,convenient,efficient or high performance of adsorption materials is one of the most attractive at the forefront research in this field.Here we report the removal performances of the iron oxides membranes?in situ Fe₃O₄ membrane?for the two common toxic cations Cd?II?and Pb?II?in apple juice.The results of the study are as follows:?1?The removal ability of the membrane for Cd?II?and Pb?II?in apple juice were studied.The results showed that the membranes exhibited high removal efficiency of⁹5%at pH 9.0 for Pb?II?of 2.5 mg/L initial concentration in room temperature,while the removal efficiency for Cd?II?was only²8%.This phenomenon was because that Pb?II?with higher electronegativity than Cd?II?can possessed different electronegativity could lead to higher affinity between Fe₃O₄ membrane and Pb?II?,resulting in better adsorption performance for Pb?II?in apple juice.In addition,the increase of temperature can increase the removal rate of Cd?II?and Pb?II?increased with temperature rising and reached36.8%and 98.9%at 55^oC respectively,which indicated that high temperature could improve the removal ability for Cd?II?and Pb?II?in apple juice.?2?Fe ions were detected in apple juice during the adsorption for Cd?II?and Pb?II?by Fe₃O₄ membrane,and the maximum concentration of released Fe ions was about 713 mg/L.This is because that the coordination between Cd?II?/Pb?II?and Fe-O groups on the surface of Fe₃O₄ membrane could have negative effect on the stability of membrane.According to the Lewis acid-base theory:Cd?II?and Pb?II?with vacant orbital were regarded as Lewis acids which could accept electron,promoting the release of Fe ions from the membrane.In addition,the concentration of Fe ions could also increase with temperature rising and reached 713.5±3.1 mg/L at 55^oC,suggesting that high temperature could result in the release of Fe ions from Fe₃O₄ membrane in apple juice.?3?Organic acids and sugars are the main components of concentrated apple juice.Organic acids in apple juice include malic acid,quinic acid and citric acid,when sugars in apple juice include fructose,glucose and sucrose.The results of SEM and AAS showed that these sugar and acid components have adverse effects on the membrane.Malic acid?20 g/L?was the main factor for the corrosion of Fe₃O₄ membrane in apple juice,which could result in the release of Fe ions for 763.0±18.7 mg/L,while sucrose could not result in Fe ions releasing.In addition,the results of SEM showed that these organic acid and sugar could result in the corrosion or blockage of the pores on the surface of the membrane,and sucrose which is not the factor for the release of Fe ions could affect the adsorption efficiency by block the pores on membrane.?4?The corrosion mechanism between Fe₃O₄ membrane and organic acid/sugars in apple juice might be due to this process:malic acid,quinic acid,citric acid,fructose,and glucose could result in Fe ions releasing by-OH.There were more Fe?II?than Fe?III?in organic acid?the results of results showed that the contents of Fe?II?were 77.6%,70.1%and 56.3%,respectively in malic acid,quinic acid and citric acid?.Adversely,there were more Fe?III?in sugar solution,suggesting that the reducibility of these acids and sugars are a important factor for the corrosion of membrane.In addition,the results of FTIR and XPS showed there was no Fe-O groups being detected,further suggesting that sucrose cannot result in Fe ions release,since sucrose had weaker reducibility because of the loss of active sites of fructose and glucose when the monosaccharide composes sucrose molecule.