Preparation of Ti-Al hydrotalcite and its adsorption performance for F-with low mass concentration in water
Bimetallic hydroxides(Ti-Al LDHs)with different n(Ti)∶n(Al)were prepared by co-precipitation method using AlCl3·6H2O and TiCl3 as raw materials and NaOH as precipitant.The adsorption performance of Ti-Al LDHS for F-with low mass concentration in simulated wastewater were analyzed,and the Ti-Al LDHs samples before and after F-adsorption were characterized by SEM,BET and XRD.The effects of Ti-Al LDHs dosage and initial solution pH on the fluorine removal capacity of Ti-Al LDHs were investigated,while the recycling capacity of Ti-Al LDHS was analyzed.The F-adsorption mechanism by Ti-Al LDHs was further speculated.The results showed that Ti-Al LDHs displayed good stability,having a uniform stacking of laminar structure,and mainly existing in dispersed amorphous form with a wide pore size distribution and a large specific surface area(108.34 m2/g).Ti-Al LDHs-1 prepared from n(Ti)∶n(Al)=2∶8 and medium pH=6 exhibited the best F-adsorption performance,and the highest fluorine removal capacity reached 63.08 mg/g with the Ti-Al LDHs-1 dosage of 0.1 g/L,water-bath constant-temperature at 25℃at a shaking speed of 200 r/min for 12 h.At room temperature and the initial solution pH=4,the equilibrium fluorine removal capacity was 47.59 mg/g,while F-removal rate reached 86.53%with Ti-Al LDHs-1 dosage of 0.2 g/L.The influence of coexisting anions(0~10 mmol/L)on the adsorption of F-were as follows:HCO3->CO32->SO42->H2PO4->Cl->NO3-.The adsorption of F-by Ti-Al LDHs-1 was more consistent with the pseudo-second-order model(R2>0.99),and the adsorption isotherm was more consistent with the Langmuir model.After four adsorption-desorption cycles,the fluorine removal capacity of Ti-Al LDHs-1 could still reach 73%of the initial capacity.The adsorption process was controlled mainly by ion exchange,electrostatic attraction and surface complexation.