Enhanced Simultaneous Adsorption Of Toxic Elements By Multiamine Functionalized Vermiculite In Aqueous Solutions

Rapid industrial growth has caused huge water contamination and serious environmental issues throughout the globe.Such contamination is due to the discharge of toxic heavy metals,among them arsenite（As）,Cadmium（Cd）,and Lead（Pb）have been the most highlighted and have remained the topic of investigation for various research studies because these they are non?biodegradable,highly carcinogenic and potentially toxic elements（PTEs）.Arsenic is not the only metalloid present in water,but it coexists with other metal ions.This situation of combined metal is not only more harmful but also difficult to control.In the last few decades,adsorption has been shown to be an economically feasible alternative method for removing toxic metals from wastewater and water supplies.The adsorption process offers flexibility in design,and operation and in many cases will produce high-quality treated effluent.In addition,the adsorption is reversible,therefore,adsorbents can be regenerated by suitable desorption process.Recently,there has been an increased attention to use natural materials for remediation.The Vermiculite（VER）is an inexpensive,nontoxic to environment,and naturally abundant aluminosilicate clay mineral,which contains hydrated exchangeable cations,primarily Ca²⁺and Mg²⁺in the interlayer.VER has a higher exchange capacity which makes it a more feasible material for higher adsorption results in contaminated water treatment.Amines are compounds which contain basic nitrogen atom（─NH₂）with a lone pair and work as functional groups.Studies reveal that VER can be easily modified for enhanced adsorption results.The scope of this study was limited to select three different primary amines surfactants namely Butylamine（BUT）,Hexylamine（HEX）and Octylamine（OCT）and three novel organoclays BUT-VER,HEX-VER and OCT-VER adsorbent materials were produced for removal of Pb（II）,Cd（II）and As（III）in water.All the experiments were performed at lab-scale.For practical applicability of adsorbents,the spiked river water from Pearl River,Guangzhou,China,was used.The adsorbents were characterized by spectroscopic,spectrometric,microscopic,and potentiometric techniques.The parameters affecting Pb（II）,Cd（II）and As（III）adsorption,including dose,p H,initial concentration,contact time,temperature,and co-existing ions(Cl,F,NO₃^-,CO₃^2-,SO₄^2-,Na⁺,K⁺Ca²⁺,and Mg²⁺)were studied.The research contents and obtained results of this study are as follow:The removal of Cd（II）,Pb（II）and As（III）by BUT-VER was studied,The kinetic data results were in better agreement with pseudo-second-order model with higher correlation coefficient（R²>0.992）.The extended Langmuir and Freundlich isotherm models were used to study adsorption system and results showed that adsorption was monomolecular layer.The BUT-VER showed an improvement in adsorption capacity in single system(Pb（II）from 86.16to 105.62 mg.g^-1),(Cd（II）from 35.13 to 38.54 mg.g^-1)and(As（III）from 9.36 to 10.42 mg.g^-1),respectively.Multicomponent adsorption system,where all these three metals were combined and analyzed.The results in multicomponent adsorption system were also improved(Pb（II）from 49.11 to 72.52 mg.g^-1),(Cd（II）:from 29.20 to 33.55 mg.g^-1)and(As（III）from6.12 to 7.35 mg.g^-1),respectively.The intra particle diffusion model results revealed that VER had only two stages of surface diffusion and adsorption equilibrium stage while BUT-VER had another intraparticle diffusion stage which was due to the variation in BUT-VER morphology.The inhibitory effect of ionic strength on Pb（II）and Cd（II）adsorption was observed in the order of Ca²⁺>K⁺>Na⁺.The As（III）removal rate increased from 79.8%to 91.4%in the presence of Ca²⁺,and from 79.8%to 94.87%in the presence of Mg²⁺cations.Ca²⁺and Mg²⁺cations enhanced the positive charges and created more active sites on the adsorbent surface,which led to higher sorption of As（III）.Based on the above result HEX-VER was used for the removal of Cd（II）,Pb（II）and As（III）.The results showed that HEX-VER owned different morphology and larger average pore diameter after functionalization,resulting in an improved adsorption capacity.HEX-VER showed an improvement in adsorption capacity in single system(Pb（II）from 86.16 to 148.6mg.g^-1),(Cd（II）from 35.13 to 42.51 mg.g^-1)and(As（III）from 9.36 to 12.62 mg.g^-1),respectively.Multicomponent adsorption system,where all these three metals were combined and analyzed.The results in multicomponent adsorption system were also improved for HEX-VER,(Pb（II）from 49.11 to 86.16 mg.g^-1),(Cd（II）:from 29.20 to 34.51 mg.g^-1)and(As（III）from 6.12 to 9.36 mg.g^-1),respectively.The dominant mechanisms for As（III）removal were ion-exchange and complexation.After these improved results,OCT-VER was used to remove Cd（II）,Pb（II）and As（III）.After analyzing it was observed that after modification,the affinities of OCT-VER towards toxic metal ions were enhanced.In single system,maximum adsorption capacities improved(Pb（II）from 86.16 to 184.6 mg.g^-1),(Cd（II）from 35.13 to 78.26 mg.g^-1)and(As（III）from9.36 to 14.83 mg.g^-1),respectively.Multicomponent adsorption system,where all these three metals were combined and analyzed.The results in multicomponent adsorption system were also improved for OCT-VER,(Pb（II）from 49.11 to 97.16 mg.g^-1),(Cd（II）from 29.20 to 43.55mg.g^-1),and(As（III）from 6.12 to 10.11 mg.g^-1),respectively.In adsorbent regeneration experiment of OCT-VER,the removal ratio was found around 90%even after 5 consecutive cycles.exhibiting good stability and easy regeneration potential.After studying thoroughly,ion-exchange and complexation properties were the main reaction mechanism.The effect of temperature on the adsorption was studied and thermodynamic results showed positiveΔH value,revealing endothermic adsorption systems and value ofΔG°,which decides the feasibility of reaction,was found negative,indicating the reaction was spontaneous for BUT-VER,HEX-VER and OCT-VER.Furthermore,for practical applicability,BUT-VER,HEX-VER and OCT-VER were tested in real river water and removed efficiency of>99%was achieved in just 1 hr.These findings suggest that the proposed inexpensive adsorbents have the potential for practical applications of toxic metals removal from water.