| Reed as raw material,through the alkaline cooking to production black liquor,every pot had dry reed 1000g quality,alkali dosage is 20%,solid liquid ratio is 1:5,temperature-rise period is 1.5 h,time at maximum temperature is 2 h,the highest temperature is 170 ?,relieving at 110?.The method of production kraft lignin is same as the alkali lignin,sulphidity is 15%,and alkali dosage is 20%.Acid was used to extract lignin,research the effect of time,temperature,pH,the addition of lignin quantity,and different metal ion concentration of Pb2+,Cr3+ and Cd2+,and through the phenol modification;Formaldehyde modified lignin by hydroxymethylation;first hydroxymethylation,and then by phenol modified.research the effect of phenols Addition amount,reaction temperature and reaction time on adsorption.The results showed that more than 50%of the metal ion been adsorbed in 10 minutes before start experiment(Pb2+ can achieve 90%).In the reaction at the start metal ion is mainly adsorption to surface,adsorption very fast.After 20 minutes metal ions is mainly adsorption spread to the inside,adsorption speed decreases.after 60 minutes,adsorption had reached balance,in the next three hours,the adsorption efficiency little change.With the increased amount of lignin,the rest of the heavy metal ion concentration drops,but when lignin more than 1.00 g,remaining concentration decline is not obvious.With the rise of pH value,the rest of the metal ion concentration is becoming smaller,explain an appropriate pH is beneficial to adsorption.When the pH of the solution is too low,the strong competition of adsorption between the protons and metal ion exists,the adsorb metal ions efficiency descend.Temperature on lignin adsorption heavy metal ions have less influence,and from the influence of temperature on the adsorption can indirect proof adsorption is a complicated process.both have physical adsorption,and chemical adsorption.When the heavy metal ion concentration is low,The ratio of the adsorption position and the metal ion number in solution is high,So adsorption efficiency is higher.And solution concentration increase has reached saturation,so adsorption capacity is no longer increases.Taken together,alkali lignin adsorption efficiencies is superior to kraft lignin.lignin adsorption heavy metal ions is good accord with adsorption dynamics,also accord with basic Longmuir single molecule layer absorption theory.Modified lingin adsorption heavy metal ions results show that:the alkali lignin after phenol modification,compared with alkali lignin,Adsorption rate obvious improvement,Pb2+Removal rate from 92.4%rise to 97.8%,Cd2+ Removal rate from 44.5%rise to 63.8%,Cr3+Removal rate from 43.4%rise to 62.5%.Before modification with phenol,lignin hydroxymethylation by formaldehyde,three kinds of modified products Adsorption rate are obvious improvement.by FT-IR analysis,Because of lignin structure unit exists phenol unit,in alkaline conditions,condensation reaction between ortho or para hydrogens of phenol and?-hydroxy at lignin's side chain,bring in phenolic hydroxyl and improve dielation to metallic ions,after hydroxymethylation,formed hydroxymethylation lignin,further improve the active site,can more fully react with phenol,and further improve the phenolic hydroxyl group,so increase the lignin adsorption ability.From the result of the modified lignin adsorb Metal ions,improve the alkali lignin Phenolic hydroxyl group is benefit to adsorb Metal ions. |
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