Different Insights into Silicate Rectorite Modification and Its Role in Removal of Heavy Metal Ions from Wastewater

Abstract

In the field of water management, the separation of metal contaminants from wastewater is very important and challenging. This study systematically investigated the effect and underlying mechanism of silicate rectorite (REC) on the removal of heavy metal ions (Cr(VI) and Pb(II)) from wastewater. The adsorption and removal capacity of REC was further improved by its novel modification with ferric chloride hexahydrate. Compared to natural REC, the modified rectorite (Fe-REC) showed comparatively superior adsorption efficiency for both Cr(VI) and Pb(II) due to the chemisorption of Fe 3+ on the REC surface as its oxidation state (Fe-O, Fe-OH, Fe-OOH). Adsorption on Cr(VI) attributed to the reaction between iron hydroxy complexes (FeOH 2+ , Fe(OH) 2 + and Fe(OH) 3 (aq)) and Cr(VI) species (HCrO 4 − and CrO 4 2− ) in the aqueous solution. This reaction was perfectly consistent with the binding energy shifts in O 1s and Fe 2p species, as reflected by XPS analysis. While, the existence of -Al-OH and -Si-OH in silicate REC slurry reacted with PbOH + colloids produced from lead ions hydrolysis to promote Pb(II) adsorption. Zeta potential after modification and removal occurred to shift positively or negatively to testify the adsorption of Fe 3+ and heavy metal ions. Freundlich and Langmuir isotherms conformed adsorption process for Cr(VI) and Pb(II), respectively.Minerals 2020, 10, 176 2 of 16 and economical approach that is widely used in wastewater treatment procedures. In adsorption, a variety of adsorbent including activated carbons, clay mineral, biomasses and synthetic polymers was employed [8,[10][11][12][13]. However, common adsorbents such as activated carbon are expensive, thus some natural resources such as polysaccharides, fly ash and clay have attracted much attention due to their low cost and easy access. In this series of materials, rectorite (REC) was applied more and more in pollutant adsorption from sewage owing to its low cost, high ion exchange capacity and relatively large specific area [14][15][16][17]. It is a sort of rare regularly interstratified silicate and similar to kaolinite. Its special structure is alternate pairs of dioctahedral mica-like layer (non-expansible) and dioctahedral smectite-like layer (expansible) existing in 1:1 ratio. There are some cations (Na + , K + and Ca 2+ ) and hydrated cations with exchangeability, which can enlarge its interlayer distance by intercalating cations or polar molecules existing in the interlayer regions.Over several decades, there are more and more investigations on the adsorption of metal ions by REC or its synthesis [17][18][19][20][21]. For example, Mei et al. [17] and Zhao et al. [22] studied separately the adsorption behaviors of Pb(II) by Ca-rectorite and Sr(II) by Na-rectorite as a function of different environmental parameters including the influence of pH, temperature, ionic strength and humic acid (HA) under ambient conditions. Both of them found that the adsorption results of heavy metals were intensely decided by pH and ionic strength and the...

A novel Iron(III)-based MOF: Synthesis, characterization, biological, and antimicrobial activity study

“…As well, the spectrum showed two doublets' peaks appeared at 710.69 eV for Fe 2p3/2 and 725.26 eV for Fe 2p1/2. These main Fe 2p peaks confirmed the oxidation state of Fe 3+ in the MOF sample [38,56]. Figure S5 shows the O 1s peaks region located at 531.14, 531.93, and 533.06 eV [57][58][59].…”

Synergistic Effect of Frequently Found Ions in the Flotation of Pb-Zn Sulfide Ores on Air/Water Interface

“…Meanwhile, the pH of the APWs was close to the pH of pure water, and therefore the experiments in this study were carried out at the natural pH of 6-7, as seen in Table 1. It is seen from the literature that at these pH values, most of this medium exists in the form of ions [34][35][36][37][38][39][40].…”