Selective Separation Of Borate Ions In Water
SELECTIVE SEPARATION OF BORATE IONS IN WATER
WITH THE USE OF A HYDROUS ZIRCONIUM OXIDE
V. Atamaniouk, T. Mal’tceva, V. Beljakov
V.I. Vernadskii Institute of General and Inorganic Chemistry, Ukrainian National Academy of Sciences, Palladin avenue 32-34, 03680 Kyev, Ukraine
Ukraine possesses only hydrous mineral raw boron reserves. There are underground mineral waters in Carpathians and the Crimea and brines of some lakes. Boric acid concentration in Carpathian mineral waters varies in range 40–530 mg/dm3 and brines of Sivash Lake contain 13 – 35 mg/dm3 of boron. On the other hand, the increased concentration of boron in water used for irrigation of crops has long been recognized as an important toxic factor. There is currently no simple method of boron removal from waste water. Boron removals by conventional biological treatment, chemical coagulation has improved to be ineffective. However, the ion-exchange method is applied as the most suitable removal method.
The present study was undertaken to investigate boron removal from the mineral, sea, waste waters, brine and bittern. An inorganic sorbent, hydrous zirconium oxide (HZO) was selected for the present work. Experimental results show that the ion-exchange operations are effective in removing boron from the all kinds of water solutions.
Capacity of a series of metal hydroxides (Аl, Lа, Тi, Fе, Zг) to adsorb boron from seawater with the sum of salts 18.22 g/dm3 and concentration B2O37.9 mg/dm3 was studied. On efficiency of a sorption the investigated hydroxides could be placed in a raw:
ZгO2 > Lа2О3 > ТiO2 > Fe2О3> Аl2О3.
The H3BO3 sorption dependence vs. рН represents an inverted, U-shaped curve. Sorption begins at рН ≈ 3 then, with increasing рН it increases, reaching a maximum at рН ≈ 9, and again decreases. At temperatures 25 – 96 °C the maximum of an adsorption corresponds to value of a constant of the first stage of boric acid dissociation (pKs = 9,2). The HZO can absorb even to 16 % В2О3
in relation to dead weight. Practically complete extraction of boron (98 %) is reached at relation ZrO2: В2О3 = 400. The decreasing sorbate capacity HZO in seawater and brine as contrasted to solution Н3ВО3 with the same concentration is insignificant and consists of 5 – 20 %. The obtained results indirectly indicate that the extraction of boron by HZO is a result of chemical interaction with formation boron - zirconium compounds.
Thus, hydrous zirconium oxide can represent itself as sorbent of connections of boron from concentrated solutions, marine and waste water and natural brines.
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