| In this work, the applicability of chitosan modified by Ln3+ (Lanthanum,Praseodymium, Neodymium) as adsorbents for the remova l of excess fluoride ionsfrom water is studied. The synthesis conditions of Ln3+ incorporated chitosan areoptimized as: the dose of chitosan is 1.0 g·L-1, the dosage of Ln3+ is 0.015 mol·L-1, thepreparing time is 68 h. From the XRD, FTIR specture, SEM ima ges, it can beobserved that the hydrogen bonding of intermolecular and intramolecular is weakened ,the crysta l structure is destructed and the particle amorphism structure is formed. TheLn(H2O)n3+ can chelated with C-3 hydroxyl groups and C-2 amino groups to form the5-element loop. The unsaturated complex is formed when Ln3+ is loaded into chitosanmolecular, F- can excha nge with OH- of water molecular and other ions don't has thesame ability, so the adsorbent has higher selectivity adsorption capability.The treatment conditions are optimized: pH value is 7, water temperature is 323 K,stirring speed is 400 rpm, contact time is 60 min, particle size is 0.1 mm,deacetylation of chitosan is 95%. A salt rejection against the water containing F- of 20mg·L-1 was 99% at the dosage of adsorbent was only 1.2 g·L-1, and the resid ualconcentration of F- is 0.98 mg·L-1, lower tha n 1.0 mg·L-1, which is restricted by WHOand Standard for Domestic Drinking Water. The drinking water contains severa lcommon other anions, which can compete with F- in the sorption process, from theadsorption experiment results, the CO32-, HCO3-, PO43-, SO42-and Cl- ions showsnega tive effect on the remova l of fluoride , the remova l efficiency could be decreased28.5%, 19.1%, 17.6%, 14.3%, 9.8%, respectively, and the order is CO32-＞HCO3-＞PO43-＞SO42-＞Cl-. The used adsorbents could be regenerated in 24 h by 0.4 g·L-1 ofsodium hydroxide , and the remova l efficiency is reduced from 98% to 67% after it isregenera ted four times, it can be reused in applicability.The equilibrium sorption data are fitted reasonably well for Redlich-Petersonisotherm model, the ma ximum equilibrium sorption of CTS-Nd, CTS-Pr and CTS-Lahave found to be 42.3, 39.7 and 39.5 mg·g-1. The qe,cal obtained from pseudo-first orderand pseudo-second order accord well with the qe,exp from the experiments, and have no significa nt difference between two groups (p＞0.05). The initia l sorption rate of CTSNd,CTS-Pr and CTS-La are 0.008, 0.009 and 0.012 g·g-1·min-1 at 323 K, and thesorption process is complex, both the boundary of liq uid film and intra-particlediffusion contributed to the rate-determining step. The activation energy (E) obtainedfrom Arrhenius equation is 11.583, 8.286 and 8.333 KJ·mol-1, which is lower tha n 42KJ·mol-1, the adsorption process is physicosorption.The results of subacute toxicity test shows that it has no any side effects on behavior,feed and water intakes, physiochemica l parameters and histology of the rats, when theconcentration of La3+ is lower tha n 106 mg·L-1, Nd3+ lower tha n 260 mg·L-1, Pr3+ lowertha n 180 mg·L-1.The water sampling from Damujia town in Gaomi area containing high fluorideconcentration, it could be removed effectively by conducting the dosage of adsorbentof CTS-Ln. 3# and 4# water containing fluoride ions and anions simultaneity, which is34 times higher tha n the five class of water. When the dosage of adsorbent is 7.58g·L-1, the resid ual concentration of F- is 0.98 mg·L-1, lower tha n 1.0 mg·L-1. Thepreparing cost and running cost of CTS-Ln (CTS-La, CTS-Nd and CTS-Pr) is￥0.220.34 and￥0.0320.056 per kilogram, respectively. When the 3# and 4# water istreated by CTS-Ln, the cost is￥0.240.448 per kilogram, the cost of other samplingwater is lower than￥0.12 per kilogram. The cost of CTS-La is the cheapest and isfeasible to apply in practice.Fluord ie from drinking water can be removed by CTS-Ln, it can minimize thehaza rdous of flurodide water, and ma ximize the utilizing the chitosan obtained fromseafood processing wastes. So, the use of CTS-Ln as adsorbent would be profitablyto socia l, economic and ecological environment.
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