Evaluation of boron removal from water by hydrotalcite-like compounds.
Layered double hydroxides (LDHs) or hydrotalcite (HT)-like compounds with different kinds of metal ions (Mg-Al and Mg-Fe) in the brucite-like sheets were prepared and their adsorption properties were studied in the boron removal from aqueous solution under laboratory conditions. The hydrotalcites were synthesized by the coprecipitation method and were characterized by chemical analyses, X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR) and specific surface area measurements (BET). The affinity of these materials with a mixture of B(OH)(3) and B(OH)(4)(-) was studied as a function of contact time, initial pH of the solutions, HT quantity and B concentration (adsorption isotherms). It was found that 120 min is enough time for the equilibrium state to be reached in boron adsorption. Boron removal was independent of the initial pH of the solutions because of the high buffering capacity of the LDHs. On the other hand, the adsorption capacity increases with increasing the adsorbent quantity. The adsorption isotherms, described by the Langmuir model, are of L-type, suggesting that B(OH)(4)(-) is adsorbed preferentially on HT-like materials. Besides, Mg-Al hydrotalcites showed higher adsorption capacity than Mg-Fe. We proposed that in Mg-Al hydrotalcites, the boron removal occurs by both adsorption on external surface and ion exchange, whereas for Mg-Fe it occurs only by surface adsorption. After treatment of a solution containing 5.2 mgBl(-1) with Mg-Al hydrotalcites the final boron concentration reached the recommended limit by WHO for drinking water (0.5 mgl(-1)).
Ferreira
Odair Pastor
OP
LQES-Laboratório de Química do Estado Sólido, Instituto de Química, Universidade Estadual de Campinas, UNICAMP, Cidade Universitária Zeferino Vaz, s/n, C.P. 6154, CEP 13083-970, Campinas, SP, Brazil. odair@iqm.unicamp.br
de Moraes
Sandra Gomes
SG
Durán
Nelson
N
Cornejo
Lorena
L
Alves
Oswaldo Luiz
OL
D000327:Adsorption; D000536:Aluminum Hydroxide / Q000737:chemistry*; D001896:Boron Compounds / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008276:Magnesium Hydroxide / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis*; D018508:Water Purification / Q000379:methods*; D014881:Water Supply / Q000592:standards
D001896:Boron Compounds; D014874:Water Pollutants, Chemical; C010467:hydrotalcite; D000536:Aluminum Hydroxide; D008276:Magnesium Hydroxide