A comparative study of two kinds of defluorinating agents for removal of fluoride in drinking water / 中华地方病学杂志

ABSTRACT

Objective To compare the effectiveness of two kinds of defluorinating agents (bone char and modified clay) for removal of fluoride in drinking water,and to analyze their application feasibility in small towns.Methods Influencing factors on defluorinating efficiencies of the two kinds of defluorinating agents under the same conditions were studied,namely the effects of adsorption time,temperature,pH,common anions and cations,and solid-liquid ratio on defluorinating efficiencies were studied.The defluorinating efficiencies of the two kinds of defluorinating agents were validated by original groundwater in Jilin Province.The homemade bone char defluorinating agent and modified clay defluorinating agent were regenerated by NaOH and Al2(SO4)3,respectively,and their regeneration abilities were investigated.Results The adsorption data of the two kinds of defluorinating agents were fitted Langmuir model well,and the maximum adsorption capacities were 10.225 g/kg(bone char) and 0.587 g/kg(modified clay).The effect of temperature on defluorinating efficiencies was limited,with increasing temperature(10-35 ℃),the adsorption capacity of bone char and modified clay for fluoride ranged from 1.568 g/kg to 1.598 g/kg and 0.423 g/kg to 0.470 g/kg,respectively.Fluoride could be easily removed under low pH conditions,with increasing of pH(4-10),the adsorption capacity of bone char and modified clay for fluoride decreased from 1.598 g/kg to 1.523 g/kg and 0.724 g/kg to 0.320 g/kg,respectively.The defluorinating efficiencies were improved by common cations(Ca2+) in groundwater,and the adsorption capacity of bone char and modified clay for fluoride increased to 1.713 g/kg and 0.485 g/kg,respectively.Whereas,the defluorinating efficiencies were inhibited by common anions(HCO3-,SO42-) at a certain degree,and the adsorption capacities of bone char and modified clay for fluoride were decreased to 1.158 g/kg(HCO3-) and 0.237 g/kg(SO42),respectively.Defluoridation bone char could be regenerated by soaking in NaOH,and modified clay by immersion in Al2(SO4)3.The adsorption capacities of the two defluorinating agents that had been regenerated for three times still reached 94.6％ and 97.3％ of their original capacities.Conclusions Both of the homemade bone char defluorinating agent and modified clay defluorinating agent have good defluorinating efficiencies and can be regenerated for many times,which are perfectly suitable for application in small towns since they are simple and can be easily applied.The homemade bone char defluorinating agent is suitable for family drinking water and the homemade modified clay defluorinating agent would be more suitable for centralized drinking water.