Research On Thallium Removal From Wastewater

In recent years, several thallium pollution incidents occurred in our country has attracted the attention to thallium.Thallium is a kind of heavy metal which can damage the nervous system.Due to the hypertoxicity of thallium,It is very urgent to search the effective and low cost method to treating wastecontaining thallium. Several treating method of the wastewater containing thallium were explored in this article in view from three aspects respectively,which were the enrichment of ferns, the adsorption of carbonized biomaterials, the adsorption of manganese oxide generated in-situ.Thallium enrichment ability of several ferns was explore by hydroponic method. Manganese oxide generated in-situ in three ways.The first way was using air to oxidate Mn(NO3) 2 directly under the condition of alkaline(MOF-1).The second way was preparation by potassium permanganate and manganese tailings which dissolute by acid(MOF-2).The third way was preparation by reaction of the air and manganese tailings which dissolute by acid under the alkaline condition,basing on the second method(MOF-3).Manganese oxide generated in-situ in three ways was removed the thallium in water. The preparation of two biological adsorbent were using rice platycodon and grapefruit peel as raw material, which carbonized directly in the air.Tl(Ⅰ)removal by three governance approach and the removal mechanism were explored preliminary,as well as the removal influence.The results showed that:(1)Thallium was enriched by Pteris vittata, Cyclosorus interruptus, Nephrolepis cordifolia,Lygodium scandens;The faster absorption of heavy metal was found in larger biomass and in the beginning of cultivating,which slowed down gradually as the culturing time extended;Pb,Cd produced competitive adsorption to Tl absorption on ferns,where Pb preformed the optimal absorptive capacity toward fern, fallowed by Cd.The heavy metals absorbed by Cyclosorus interruptus was mainly enriched in the root,which would release back to the soil when soaking and leaching by acid water.(2)Lots of organisms of –COOH and –OH and Si O2 wasfound on the carbonized biological materials by FT-IR,which contributed to the adsorption of Tl(Ⅰ).The specific surface area of carbonized straw(CS)and carbonized grapefruit peel(CG) was 4.37 m2?g-1and 2.66 m2?g-1.In the p H = 6, the optimal dosage of CS and CG to remove 10.0 mg?L-1Tl(Ⅰ) from water was 1:200and 1:100(solid-liquid ratio); Under acidic conditions,removal of Tl(Ⅰ) on the carbonized biological materials was non-significant while it obtained good effect in both neutral and alkaline condition.The coexistent of Ca(Ⅱ),Mg(Ⅱ), Cd(Ⅱ), Pb(Ⅱ), Cr(Ⅲ) had no significant impact on the Tl(Ⅰ) removal under alkaline conditions. Tl(Ⅰ) adsorption on CS and CG were fitted well by the Lagergren pseudo-first-order equation,which achieved the adsorption equilibrium in about 20 min;The absorption were fitted well by the Freundlich isothermal adsorption equation and the maximum adsorption capacities of CS and CG were 30.5 mg?g-1 and 25.6 mg?g-1respectively. Two of carbonized biological materials removed thallium from actual industrial wastewater by 92.0%.(3)Tl(Ⅰ) removal in water by manganese oxide generated in-situ in three ways reached 98.5%,of which the optimal dosage of MOF generatedwere2.50 mmol?L-1,0.500 mmol?L-1,5.00 mmol?L-1 respectively. Thallium absorption on MOF-1 and MOF-2 were fitted well by the Freundlich isothermal adsorption equation and the maximum adsorption capacities were 91.9 mg?g-1 and 305 mg?g-1respectively. Thallium was removed completely in 10 min by MOF-1,while the adsorption reached equilibrium at 2 h for MOF-2 and fitted well by the Lagergren pseudo-first-order equation.Tl(Ⅰ) removal of MOF-1 increased gradually as p H increases, which the optimum p H was 12,while it obtained had perfect efficiency on the Tl(Ⅰ) adsorption in p H=2~13 for MOF-2. Cd(Ⅱ), Pb(Ⅱ), Cr(Ⅲ) had no significant impact on the Tl(Ⅰ) removal,while Ca(Ⅱ),Mg(Ⅱ) produced competitive adsorption. Adding a small amount of hydrogen peroxide increased the efficiency of removal of MOF-3 which removed Tl by 98.5%.The result showed that manganese oxide generated in-situ by the second way(MOF-2) producted the optimal adsorption efficiency.The results of characteristics using XRD,FT-IR,SEM and BET showed that the specific surface area of manganese dioxide generated(MOF-2)was 196 m2?g-1,with surface hydroxyls and micropores.(4)Three methods of removing thallium from wastewater was studied, the raw materials of which were,extensive,low cost,environmental and highly effective. Tl(Ⅰ)adsorption capacity of manganese oxide generated in-situ by chemical method was optimal among them.