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 Fe3+ 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 (FeOH2+, Fe(OH)2+ and Fe(OH)3(aq)) and Cr(VI) species (HCrO4− and CrO42−) 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 Fe3+ and heavy metal ions. Freundlich and Langmuir isotherms conformed adsorption process for Cr(VI) and Pb(II), respectively.
Highlights
A long-standing problem, heavy metal ions contaminations from wastewater, is being in dire need of a solution to be solved thoroughly due to their biological accumulation and higher toxicity even at minute concentrations
Modification results were evaluated by the ability of modified rectorite to adsorb Cr(VI) ion in the solutions
If REC was modified for a longer time, less and less Cr(VI) ions were adsorbed on the REC surface making the adsorption rate deteriorated
Summary
A long-standing problem, heavy metal ions contaminations from wastewater, is being in dire need of a solution to be solved thoroughly due to their biological accumulation and higher toxicity even at minute concentrations. Hexavalent chromium is a kind of strong oxidant and highly soluble heavy metal with carcinogenic, mutagenic and teratogenic substance for human [1,2]. While Pb(II) acts as one of the most harmful heavy metals [4], plumbism by accumulation in human body can result in damages in brain, nervous, metabolic and reproductive system, even trigger sickness or death [5,6]. The bulk of these contaminations as effluents are discharged from several industries, including mining, batteries, textiles, metal plating, etc.
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