Effects Of Biochar And Its Aging Process On The Adsorption Mechanism Of Cadmium And Ammonium

In this study,three kinds of agricultural solid wastes(pig manure,pig resdule rice straw)were pyrolyzed at five temperatures(300,400,500,600,700?)using two sieving treatments(before and after pyrolysis)to produce 30 kinds of biochar.The physicochemical properties,surface characterization and cadmium adsorption capacity of biochars with different treatments were investigated.And the adsorption mechanisms of biochars to cadmium and ammonium were quantify.4 kinds of aging biochar(ORC400,ORC700,HRC400,HRC700)were prepared by high temperature aging(temperature 50? humidity 40%,one month)and oxidation(15%H2O2).The physicochemical properties,surface characterization and adsorption capacity of biochars before and after aging were investigated.The results showed that:(1)Pyrolysis temperature and raw materials were the key factors that affect physicochemical properties biochars.With the increase of pyrolysis temperature,the ash content,pH value and specific surface area of biochars increased gradually.At the same pyrolysis temperature,the ash content of pig manure,pig manure residue biochars was higher,while the pH value and BET specific surface area were opposite.(2)Raw mater:ials was the key factors that affect cadmium adsorption capacity of biochars.The adsorption capacity of rice straw biochars was significantly higher than that of pig manure,pig manure residue biochars.With the increase of pyrolysis temperature,the adsorption capacity of rice straw biochars increased significantly.There was no distinction on the physicochemical properties and the cadmium adsorption of biochar before and after seiving.(3)Correlations between the yield and ash content of different biochars were significantly negatively correlated,and yield showed highly significant and positive correlation with H/C.The ash content of biochars was positively correlated with pH.The cadmium adsorption capacity of biochars was negatively correlated with yield and H/C molar ratio,while positively correlated with pH value,ash content and BET specific surface area.(4)The isothermal adsorption data of RC400,RC700 to cadmium and ammonium was well described by Langmuir model.And the pseudo-second-order kinetic model was best fitted the kinetic adsorption data.There was competitive adsorption between ammonium and cadmium,when the concentration of ammonium was reached to 50 mg/L,the cadmium adsorption capacity of biochars decreased significantly,indicating that cadmium and ammonium shared the same adsorption sites.(5)The pyrolysis temperature has effect on the adsorption capacity and adsorption mechanism of cadmium and ammonium.The main adsorption mechanism of RC400 on cadmium is cation exchange(52.37%),while RC700 was mineral precipitation(CdCO3,61.39%).The main adsorption mechanisms of RC400 and RC700 on ammonium were electrostatic adsorption(74.26%and 79.27%respectively).With the increase of pyrolysis temperature,the proportion of functional group complexation and ion exchange decreased.(6)The pH value of biochar decreased after oxidation and high temperature aging,and the pH value of oxidized biochar decreased greatly.Compared with fresh biochar,the H/C,O/C and(O+N)/C of aged biochar increased,and the biochar changed more obviously at high temperature aging.(7)The adsorption of cadmium and ammonium by oxidized biochar(ORC400,ORC700)was greatly reduced.The cadmium adsorption capacity by high temperature aging(HRC400,HRC700)was decreased to a certain extent,while the ammonium adsorption capacity was obviously improved.