Abstract
Critical Flocculation Concentration (CFC) is an important quantity because allows to know the optimal amount of flocculant required to remove (adsorb) specific quantities of metal ions in aqueous solution allowing to reduce both, the flocculation time and the excess of unreacted flocculant; this unreacted material produces, by itself, an additional contamination. The results reported here show that the standard Schulze-Hardy-Rule (SHR), based only in the valence z, is not longer valid to obtain the right values of CFC. In this work it is reported a correct determination of CFC for di- and tri-valent ions using different types of silica nanoparticles. Both, the initial pH slope (-pHo) and the valence z are required to determine correctly the CFC. The proposed modified version for CFC is CFC ∝ [(-pHo)z]−1.
Highlights
The removal of heavy metal ions from water bodies contaminated by industrial wastes, is an important health problem because the reserves of drinkable water are reducing drastically by the increment in the population and in the industrial activity (Joseph et al, 2019; Mishra et al, 2020); in addition to this is the high toxicity of these ions which affect the human health, living resources and ecological systems, including groundwater contamination; the remediation of these contaminated water bodies is highly recommended and urgent (Vardhan et al, 2019)
Two types of commercial silica nanoparticles were used as adsorbent: a) Aerosil A130VS (Degussa, AG) and b) Aerosil R972 (Degussa, AG); the A130VS nanoparticles were modified with TEOS using the sol-gel method (Hernandez and Rodrıguez, 1999) to increase the number of OH groups on the surface and its adsorption capacity; this reaction can be schematically written as: ðA130VSÞ À OH þ Si À ðO À CH2 À CH3Þ4 þ 3H2O ! ðA130VSÞ À O À Si À ðOHÞ3 þ ðCH3 À CH2 À OHÞ4
For Al3þ in VS and VSþTEOS the Critical Flocculation Concentration (CFC) are reported in Figure 2; similar plots were obtained for other systems
Summary
The removal of heavy metal ions from water bodies contaminated by industrial wastes, is an important health problem because the reserves of drinkable water are reducing drastically by the increment in the population and in the industrial activity (Joseph et al, 2019; Mishra et al, 2020); in addition to this is the high toxicity of these ions which affect the human health, living resources and ecological systems, including groundwater contamination; the remediation of these contaminated water bodies is highly recommended and urgent (Vardhan et al, 2019). The high toxicity and the accumulating effect of these ions affect all living creatures included human beings producing severe harmful effects (Ayangbenro and Babalola, 2017; de Angelis et al, 2017; Klein, 2019; Mehmood et al, 2019). Al was included first because is the only trivalent cation considered here, and second because it is the most abundant metal on earth and posses a wide range of industrial applications; the people has a significant contact it and this metal is not present in the human body (Ramrakhiani et al, 2017; Savvilotidou et al, 2014)
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