Synthesis Of Novel Ionic Liquids And Experimental Study On Extraction Of Heavy Metal Ions In Industrial Effluent

With the rapid economic growth and industrial revolution,heavy metal contamination in water bodies is becoming more prominent.One of the primary sources of heavy metal contamination in the aquatic environment is wastewater discharge.Liquid-Liquid extraction is an effective method to remove toxic and harmful heavy metals from the wastewater.As a result,the development of innovative and effective materials has become a research priority in wastewater heavy metal treatment.This research aims to remove heavy metals from wastewater using novel and efficient adsorbents to contribute to green chemistry.The main content of this study includes synthesis and characterization of five new ionic liquids,selecting a suitable ionic liquid for extraction of heavy metal ions based on liquid-liquid extraction system,study on influencing factors that affect the extraction efficiency of ionic liquids,response surface methodology used to enhance the extraction conditions by optimization based on box-behnken design,comparative study of novel ionic liquids extraction behavior and back extraction efficiency and the ecotoxicity analysis of ionic liquid by acute microtox assays.The main results are as follows:1)First time five novel ionic liquids based on cheap and biodegradable fatty acid oleate anion with different imidazolium cations are synthesized by metathesis synthesis method namely 1-butyl-3 methyl imidazolium Oleate（[BMim][Oleate]）,1-hexyl-3-methyl imidazolium Oleate（[HMim][Oleate]）,1-octyl-3-methyl imidazolium Oleate（[OMim][Oleate]）,1-tetradecyl-3 methyl imidazolium Oleate（[TDMim][Oleate]）and 1-hexadecyl-3-methyl imidazolium Oleate（[HDMim][Oleate]）ionic liquid respectively.The metathesis method is a reaction process in which anions and cations exchange partners.Synthesis experiments depend on the reaction temperature,time,salts molar ratio,and amount of solvents.Ionic liquids substituted by the longer alkyl chain were synthesized at higher temperatures.[BMim][Oleate]ionic liquid obtained with the yield of 87%when the relative salts molar ratio 1:1.1,reaction time 6h-8h and temperature 40°C was maintained.[HMim][Oleate]ionic liquid was acquired with 79%yield at 37°C reaction temperature,molar salts ratio1:0.93 and time interval of 9h-12h.[OMim][Oleate]ionic liquid with 95%yield was procured when the molar salts ratio 1:0.96,reaction time 10h-15h and temperature kept at 65°C.[TDMim][Oleate]and[HDMim][Oleate]ionic liquids was gained with the yield of 65%and 97%at molar salts ratio 1:1,time 11h and 16h and temperature set at75°C and 65°C respectively.The physicochemical characterization of novel ionic liquids is extensively examined by different analytical techniques,including ¹H and ¹³C NMR analysis,viscosity,density and water content measurements at the temperature range of 10°C to 90°C,thermal stability observed at 35°C to 600°C and melting behavior detected from-90°C to 27°C.2)Five synthesized oleate base novel ionic liquids were tested in a liquid-liquid extraction system to examine their extraction efficiencies towards heavy metal ions zinc,copper,and cadmium of 1000 mg/L concentration with a phase ratio of 1:10 for selecting a suitable ionic liquid at temperature 25°C.Liquid-Liquid extraction is a method in which a solute can be transmitted into an immiscible absorbent as well as an extraction mechanism base on the mass transfer rate of solute.During the extraction analysis,a prominent color changing of ionic liquids were observed due to their promising extraction abilities for heavy metals.Based on the observed results,two ionic liquids[OMim][Oleate]and[HDMim][Oleate]which showed admirable removal capabilities more than 90%within 60min were selected for further extraction analysis.Different influencing factors were scrutinized in the absence of chelating agents which affects extraction efficiencies.Investigated the effects of p H from 0.5 p H to 8p H,effects of extraction time from 15min to 120min,effects of temperature on extraction efficiency from 298K to 333K,effects of different adsorbent（ionic liquid）amount from0.1g to 2g and effects of heavy metal ions concentration on removal abilities from 1mg/L to 2000 mg/L.The maximum removal efficiencies for heavy metals around 96%were observed at p H 6.5-7.0 with the amount of extractant 0.5g,heavy metals concentration 500 mg/L,temperature 333K and an equilibrium state was developed with 90 min contact time of novel ionic liquids,respectively.Response surface methodology based on Behnken Box design was used to optimize the extraction behavior and results revealed that at p H 6.7&6.9 and 0.77g absorbent amount,get the maximum extraction efficiencies towards heavy metal ions by[OMim][Oleate]ionic liquid and[HDMim][Oleate]ionic liquid,respectively.The extraction mechanism study was based on ion pairing which examined by equilibrium slope methodology,both molecules cation and anion of ionic liquids were involved in the removal of heavy metal ions from the solution to form chloro complexes.3)The regeneration method and efficiencies of both selected oleate base novel ionic liquids were studied.Ionic liquids showed promising regeneration and reusability to extraction and back-extraction of zinc,copper,and cadmium heavy metals in four and five cycles.Five different eluents such as HCL,HNO₃,H₂SO₄,Na OH,and Na₂C₂O₄ with their mole concentrations range from 0.1M to 1M were applied as stripping solution for the regeneration of ionic liquids,and from all these eluents,sulphuric acid（H₂SO₄）showed good and auspicious behavior.[OMim][Oleate]ionic liquid was regenerated with 1M H₂SO₄ within 1h at room temperature and then washed by deionized water for further reusability experiments up to five cycles extraction and back extraction.At fifth regeneration cycles,the extraction efficiency of[OMim][Oleate]ionic liquid on zinc,copper and cadmium was 89%,95%and 93%,respectively.Meanwhile,1M H₂SO₄ has been used as a regeneration solution for[HDMim][Oleate]ionic liquid up to four cycles of reusability（extraction and back-extraction）and at fourth regeneration cycles,removal abilities of[HDMim][Oleate]ionic liquid for heavy metals was 89.63%,92.96%and 91.28%,respectively.The promising regeneration performance of oleate base novel ionic liquids was demonstrated and held the comparative study of extraction and back-extraction with literature that endorsed this study’s decent results.4)Ecotoxicity behavior of two selected novel ionic liquids towards aquatic organism（photobacterium phosphoreum,also called Vibrio fischeri）in this study was examined by acute microtox assays method in terms of 50%effective concentration(EC₅₀).The ecotoxicity analysis showed that[OMim][Oleate]ionic liquid is a more environment-friendly extractant than[HDMim][Oleate]ionic liquid.[HDMim][Oleate]ionic liquid is highly toxic towards vibrio fischeri after 15 min exposure.The results indicate that a careful usage of ionic liquids needs to be considered,and further studies are required to improve their environmental properties,especially[HDMim][Oleate]ionic liquid.This paper has 69 Figures,23 tables,218 references.