Treatment of aqueous solutions containing nickel using crandallite‐type compounds

Abstract

The removal of nickel from aqueous solutions streams has been investigated using an artificial amorphous crandallite-type compound, CaAl 3 (OH) 6 (HPO 4 )(PO 4 ) (Ca-crandallite), synthesized in our laboratory. Equilibrium ion-exchange isotherms in an aqueous medium of Ca 2+ /Ni 2+ at different pH values at 293 K have been determined. The experimental equilibrium data were satisfactorily correlated using a Langmuir-type empirical equation. At low pH values, the hydrogen ion competes with the heavy metal cation and the percentage removal of metal declines. It was found that the operating capacity of Ca-crandallite with respect to the metal ion increased with the pH of the solution, in accordance with a second-degree polynomial equation. However, the pH should not be allowed to rise to levels at which chemical precipitation as nickel hydroxide would occur, with 7.00 the highest value tested. Taking into account the variation of operating capacity with pH, the system exhibited a unique separation factor, namely all the experimental points can be described by a unique isotherm in a dimensionless form. The Ca-crandallite showed a high capacity, 2.176 meq g −1 , for the exchange of Ni(II) from nickel nitrate solutions and the rate of exchange of metal increases with increasing solution temperature due to the enhancement of effective intraparticle diffusivity.

Removal of nickel from effluents by chelating ion exchange

“…For heavy metal ion–sodium ion exchange there is almost no pH change, in fact, less than 0.5 pH unit. In this case, the maximum adsorption capacity remains constant in the pH range 4.5–6.0 according to the present work and others 28…”

“…It is well established that the effluent solution pH can affect the exchange capacity of ion exchange resins for metal ions 28. In order to assess the effect of pH a series of isotherms were analysed at different pH values.…”

Thermal stability of the waylandite-structured nanocrystalline BiAl3(PO4)2(OH)6

“…The relevance of obtaining and studying such phosphates, in particular, lies in the prospects of using them as matrices for toxic and radioactive waste due to their structural features, thermal stability and high ability to ionic substitution of toxic Hg, As, Tl, Sb, Cr, Ni, Ca, radioactive K, Sr, Th, U, Ra, Pb and rare earths [10][11][12][13][14]. Data on the synthesis of these compounds are scanty and have a number of shortcomings.…”