Macroscopic and Microscopic Investigation of Ni(II) Sequestration on Diatomite by Batch, XPS, and EXAFS Techniques

Abstract

Sequestration of Ni(II) on diatomite as a function of time, pH, and temperature was investigated by batch, XPS, and EXAFS techniques. The ionic strength-dependent sorption at pH < 7.0 was consistent with outer-sphere surface complexation, while the ionic strength-independent sorption at pH = 7.0-8.6 was indicative of inner-sphere surface complexation. EXAFS results indicated that the adsorbed Ni(II) consisted of ∼6 O at R(Ni-O) ≈ 2.05 Å. EXAFS analysis from the second shell suggested that three phenomena occurred at the diatomite/water interface: (1) outer-sphere and/or inner-sphere complexation; (2) dissolution of Si which is the rate limiting step during Ni uptake; and (3) extensive growth of surface (co)precipitates. Under acidic conditions, outer-sphere complexation is the main mechanism controlling Ni uptake, which is in good agreement with the macroscopic results. At contact time of 1 h or 1 day or pH = 7.0-8.0, surface coprecipitates occur concurrently with inner-sphere complexes on diatomite surface, whereas at contact time of 1 month or pH = 10.0, surface (co)precipitates dominate Ni uptake. Furthermore, surface loading increases with temperature increasing, and surface coprecipitates become the dominant mechanism at elevated temperature. The results are important to understand Ni interaction with minerals at the solid-water interface, which is helpful to evaluate the mobility of Ni(II) in the natural environment.

Utilization of chitosan–clinoptilolite composite for the removal of radiocobalt from aqueous solution: kinetics and thermodynamics

“…As well known, the ionic strength can influence the double electrode layer thickness and interface potential, thereby affecting the binding of the adsorbed species. It is expected that the outer-sphere surface complexes or ion exchange is more impressionable to ionic strength variation than innersphere complexes as the background electrolyte ions are placed in the same plane for outer-sphere surface complexes [26,27]. Based on the theory mentioned above and the experimental data in Fig.…”

Surface silylation of mesoporous/macroporous diatomite (diatomaceous earth) and its function in Cu(II) adsorption: The effects of heating pretreatment

“…The adsorptions of some metal ions (e.g., Ni(II) [10,11], Pb(II) [11][12][13], Cu(II) [11], Cd(II) [13] and Th(IV) [14]) and organic contaminants [15] on raw diatomite and the effects of aqueous chemistry conditions, such as pH and temperature, on the adsorptions have been comprehensively investigated. However, diatomite exhibited an ordinary adsorption capacity for these molecules or ions that was close to or even lower than those of natural zeolite [16] or clay minerals, such as kaolinite [17] and montmorillonite [17,18].…”

Sorption and desorption properties of Eu(III) on attapulgite

“…One can see that the sorption of Eu(III) to attapulgite increases quickly with increasing contact time up to 100 min, and then increases slowly with contact time. The quick sorption of Eu(III) to attapulgite suggests that the sorption of Eu(III) to attapulgite is mainly dominated by chemical sorption or surface complexation rather than physical adsorption [29]. In the following experiments, 48 h of contact time was applied to achieve the sorption equilibration of Eu(III) on attapulgite.…”