Study On Functionalized Modification And Resource Utilization Of Apple Pomace

The resource utilization of agricultural and forestry biomass not only realizes the secondary utilization of waste,but also conforms to the sustainable development strategy of China's economy.China has abundant production of apple and a large number of apple pomace is produced each year from apple processing industry.Most of the apple pomace,is discarded as garbage except for a small amount,which is used as fuel,feed or to extract pectin from it.The random pile of a large amount of apple pomace not only occupies land,but also pollutes the environment,resulting in the emission of terribly rotten smell.Therefore,proper utilization of wasted apple pomace has become imperative.Biosorption has low cost,green pollution-free,and is in line with sustainable development strategies.Therefore,it has received extensive attention in the adsorption of heavy metals and precious metals.In this paper,the apple pomace was dewaxed and purified by the soxhlet extraction,then the adsorbent material for treating precious metals was prepared by graft modification of C-2,C-3,C-6 active-OH groups on the apple pomace cellulose glucose unit(AGU),and the magnetic apple pomace biochar adsorption materials were synthesized by carbonization.The main work and conclusions are as follows:(1)A new adsorbent DMTD-AP was prepared by pretreatment of purified apple pomace(AP)as raw material and modified by 2,5-dimercaptothiadiazole(DMTD).The physicochemical properties were characterized by Fourier transform infrared spectroscopy(FTIR),elemental analysis,scanning electron microscopy(SEM),thermogravimetric analysis(TG-DTG),solid nuclear magnetic(¹³C-NMR)and X-ray photoelectron spectroscopy(XPS).The results showed that the new peaks-S-S-,-C-S-C and-S-O were found in the FTIR of DMTD-AP,and the elemental analysis showed that the content of N and S in DMTD-AP increased significantly.The results of batch adsorption experiments showed that when p H=4.0,temperature was 25°C,dosage was 2.00 g/L,and contact time was 10 h,The removal rate of Au(?)by DMTD-AP in the penta-component mixture of Au(?)-Cu(II)-Pb(II)-Zn(II)-Ni(II)was98.80%,it indicated that DMTD-AP preferentially enrich the low concentration of Au(?).The adsorption equilibrium studies show that the adsorption of Au(?)is a typical BET multilayer adsorption with a maximum adsorption capacity of 176.18mg/g,186.48 mg/g and 237.33 mg/g at 25°C,45°C and 45°C,respectively.Column adsorption experiments further showed that DMTD-AP can achieve selective enrichment and separation of Au(?).The adsorption kinetics study combined with FTIR and XPS analysis showed that the presumable mechanism of Au(?)adsorption on DMTD-AP involves intra-particle diffusion and coordination.(2)Magnetic biochar was prepared by purifying apple pomace in soxhlet extraction,then immersing in Fe²⁺/Fe³⁺aqueous solution,and finally pyrolyzing a large amount of apple pomace under nitrogen protection at 600°C.The physicochemical properties were characterized by Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS)and hysteresis loop(VSM).The characterization showed that the saturation magnetization value and the Brunauer-Emmett-Teller(BET)specific surface area of MAPBC were 1.61emu/g and 37.04 m²/g.Batch adsorption studies show that MAPBC preferentially enrich the low concentration of Au(?)in the penta-component mixture of Au(?)-Cu(II)-Pb(II)-Zn(II)-Ni(II),and the maximum adsorption capacity of MAPBC for Au(?)at 25°C,35°C,45°C reached 826.45 mg/g,833.33 mg/g,833.33mg/g.Column adsorption experiments further indicate that MAPBC can selectively enrich and separate Au(?)from such a penta-component aqueous mixture of Au(?)-Pb(II)-Cu(II)-Zn(II)-Ni(II).Adsorption kinetics studies combined with FTIR,XRD and XPS analysis indicate that the possible adsorption mechanism of MAPBC to Au(?)may involve surface adsorption and chemisorption,including intraparticle diffusion,coordination,ion exchange and reduction.