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ABSTRACT
An arsenic biosorbent comprising neem leaves (NL) and MnFe2O4 particles was developed and its removal potential was investigated. Physicochemical analysis of the NL/MnFe2O4 composite (MNL) was performed for the Brunauer, Emmett and Teller surface area, Fourier transform infrared spectra (FT-IR), and scanning electron microscopy–Energy-dispersive X-ray (EDX). The following parameters were optimized: pH, biosorbent dose, contact time, temperature, and initial arsenic concentration. The optimum pH values achieved for biosorption of As(III) and As(V) were 7.0 and 4.0, respectively, when the equilibrium time was 110 minutes for both. MNL was found to be efficient with 85.217% and 88.154% biosorption efficiency at a concentration of 50 mg/L of As(III) or As(V) solution, respectively. This was also proved by the FT-IR study of arsenic-loaded biosorbent. For establishing the best suitable correlation for the equilibrium curves exploiting the procedure of the nonlinear regression for curve fitting analysis, isotherm studies were conducted for As(III) and As(V) using 30 isotherm models. The pattern of biosorption fitted well with Brouers–Sotolongo isotherm model for As(III) and Langmuir–Freundlich as well as Sips isotherm models for As(V). Dubinin–Radushkevich (D-R) isotherm studies specified that ion exchange might play a significant role. The influence of various co-existing ions at different concentrations was examined. Desorption study was performed using various concentrations of NaOH solution.
Acknowledgments
The authors thank the Indian Institute of Technology, Roorkee, India, for providing necessary facilities, and the Editor and two anonymous reviewers for their thoughtful comments.
Nomenclature
| AE | = | the energy of adsorption (KJ/mol) |
| AFS | = | Fritz–Schlunder (IV) isotherm constant ((mg/g)(L/mg)αFS) |
| aFS | = | Fritz–Schlunder (IV) model exponent |
| aK | = | Khan isotherm exponent |
| AKC | = | Koble–Corrigan parameters ((mg/g)(L/mg)nKC) |
| bB | = | Baudu isotherm constant (L/mg) |
| BFS | = | Fritz–Schlunder (IV) isotherm constant ((L/mg)βFS) |
| bFS | = | Fritz–Schlunder–IV model exponent |
| bJ | = | Jossens model exponent |
| bK | = | Khan isotherm constant (L/mg) |
| BKC | = | Koble–Corrigan parameters ((L/g)nKC) |
| bTE | = | Temkin isotherm constant corresponding to heat of adsorption (J/mol) |
| C0 | = | initial concentration of arsenic in the solution (mg/L) |
| Ce | = | equilibrium concentration of arsenic in the solution (mg/L) |
| E | = | mean free energy (KJ/mol) |
| K1 | = | Fritz–Schlunder (V) equilibrium constant ((L/mg)αFS) |
| K2 | = | Fritz–Schlunder (V) equilibrium constant ((L/mg)βFS) |
| KBS | = | Brouers–Sotolongo isotherm constant ((mg/g)(L/mg)1/α) |
| KF | = | Freundlich isotherm constant ((mg/g)(L/mg)1/nF) |
| KDR | = | Dubinin–Radushkevich isotherm constant or activity coefficient linked to mean adsorption energy (mol2/KJ2) |
| KFS | = | Fritz–Schlunder (III) isotherm constant ((L/mg)nFS) |
| KH | = | Hill isotherm constant (L/g) |
| KHE | = | adsorption equilibrium constant known as Henry constant (L/g) |
| KHK | = | Holl–Krich isotherm constant ((L/mg)nHK) |
| KL | = | Langmuir isotherm constant signifying the affinity between the adsorbent and the adsorbate molecules relating the energy of adsorption (L/mg) |
| KLJF | = | Langmuir–Freundlich–Jovanovic isotherm constant (L/mg) |
| KJ | = | Jossens isotherm constant ((mg/g)(L/mg)) |
| KJF | = | Jovanovic–Freundlich isotherm constant depends only on the temperature (L/mg) |
| KJV | = | Jovanovic isotherm constant linked to the free energy of adsorption (L/g) |
| KL | = | Langmuir isotherm constant (L/mg) |
| KLF | = | Langmuir–Freundlich isotherm constant (L/mg) |
| KLJ | = | Langmuir–Jovanovic isotherm constant (L/mg) |
| Km | = | Activated sludge model constant (L/g) |
| KMJ | = | Marczewski–Jaroniec isotherm constant (L/mg) |
| KRP | = | Redlich–Peterson isotherm constant (L/g) |
| KRPI | = | Radke–Prausnitz I isotherm constant (L/mg) |
| KRPII | = | Radke–Prausnitz II isotherm constant (L/mg) |
| KRPIII | = | Radke–Prausnitz III isotherm constant (L/mg) |
| KS | = | Sips isotherm constant related to affinity constant (mg/L)−1/mS |
| KT | = | Toth isotherm constant linked to affinity constant (L/mg) |
| KTE | = | Temkin isotherm constant corresponding to the maximum binding energy (L/mg) |
| KU | = | Unilan isotherm constant ((L/mg)bHK) |
| KVS | = | Vieth–Sladek isotherm constant (L/mg) |
| J | = | Jossens isotherm constant ((L/mg)bJ) |
| M | = | mass of the adsorbent (dry) used (g) |
| mLF | = | Langmuir–Freundlich model exponent or heterogeneity factor |
| mMJ | = | Marczewski–Jaroniec model exponent |
| mRPI | = | Radke–Prausnitz I model exponent |
| mRPII | = | Radke–Prausnitz II model exponent |
| mRPIII | = | Radke–Prausnitz III model exponent |
| ms | = | Sips model exponent |
| n | = | the number of observations in the experimental study |
| nF | = | Freundlich model exponent |
| nFS | = | Fritz–Schlunder–III model exponent |
| nH | = | Hill cooperativity coefficient |
| nHK | = | Holl–Krich model exponent |
| nJF | = | Jovanovic–Freundlich model exponent |
| nLJ | = | Langmuir–Jovanovic model exponent |
| nLJF | = | Langmuir–Freundlich–Jovanovic model exponent |
| nKC | = | Koble–Corrigan parameters |
| Nm | = | Activated sludge model exponential constant |
| nMJ | = | Marczewski–Jaroniec model exponent |
| nT | = | Toth isotherm exponent, a measure of surface heterogeneity |
| p | = | the number of parameters to be determined |
| qe | = | adsorption capacity or amount of arsenic adsorbed onto the surface of adsorbent at equilibrium (mg/g) |
| qe,exp | = | the equilibrium adsorption capacity observed from the batch experiment (mg/g) |
| qe,model | = | the prediction from the isotherm model corresponding to Ce (mg/g) |
| qmB | = | maximum monolayer adsorption capacity predicted by Baudu isotherm (mg/g) |
| qmBS | = | maximum monolayer adsorption capacity forecasted by Brouers–Sotolongo isotherm (mg/g) |
| qmDR | = | maximum monolayer adsorption capacity predicted by Dubinin–Radushkevich isotherm (mg/g) |
| qmFS | = | maximum monolayer adsorption capacity forecasted by Fritz–Schlunder (III) isotherm (mg/g) |
| qmFS5 | = | maximum monolayer adsorption capacity given by Fritz–Schlunder (V) isotherm (mg/g) |
| qmH | = | maximum monolayer adsorption capacity predicted by Hill isotherm (mg/g) |
| qmHK | = | maximum monolayer adsorption capacity predicted by Holl–Krich isotherm (mg/g) |
| qMjf | = | maximum monolayer adsorption capacity predicted by Jovanovic–Freundlich isotherm (mg/g) |
| qmJV | = | maximum monolayer adsorption capacity predicted by Jovanovic isotherm (mg/g) |
| qmK | = | maximum monolayer adsorption capacity forecasted by Khan isotherm (mg/g) |
| qmL | = | maximum monolayer adsorption capacity predicted by Langmuir isotherm (mg/g) |
| qmLF | = | maximum monolayer adsorption capacity predicted by Langmuir–Freundlich isotherm (mg/g) |
| qmLFJ | = | maximum monolayer adsorption capacity predicted by Langmuir–Freundlich–Jovanovic isotherm (mg/g) |
| qmLJ | = | maximum monolayer adsorption capacity predicted by Langmuir–Jovanovic isotherm (mg/g) |
| qmMJ | = | maximum monolayer adsorption capacity forecasted by Marczewski–Jaroniec isotherm (mg/g) |
| qmL | = | maximum monolayer adsorption capacity predicted by Langmuir isotherm (mg/g) |
| qmRPI | = | maximum monolayer adsorption capacity forecasted by Radke–Prausnitz I isotherms (mg/g) |
| qmRPII | = | maximum monolayer adsorption capacity forecasted by Radke–Prausnitz II isotherms (mg/g) |
| qmRPIII | = | maximum monolayer adsorption capacity forecasted by Radke–Prausnitz III isotherms (mg/g) |
| qmS | = | maximum monolayer adsorption capacity predicted by Sips isotherm (mg/g) |
| qmT | = | maximum monolayer adsorption capacity forecasted by Toth isotherm (mg/g) |
| qmU | = | maximum monolayer adsorption capacity forecasted by Unilan isotherm (mg/g) |
| qmVS | = | maximum monolayer adsorption capacity predicted by Vieth–Sladek isotherm (mg/g) |
| R | = | universal gas constant (8.314 J/mol K) |
| Rd | = | distribution coefficient |
| Re | = | removal efficiency |
| RL | = | separation factor or adsorption intensity |
| s | = | Unilan model exponent dependent on temperature describing the heterogeneity of the system |
| T | = | absolute temperature (K) |
| V | = | working volume of the solution (L) |
| x | = | Baudu model exponent |
| y | = | Baudu model exponent |
Greek symbols
| α | = | Brouers–Sotolongo model exponent |
| αFS | = | Fritz–Schlunder (V) model exponent |
| αRP | = | Redlich–Peterson isotherm constant (L/mg)βRP |
| βFS | = | Fritz–Schlunder (V) model exponent |
| βRP | = | Redlich–Peterson model exponent |
| βVS | = | Vieth–Sladek equilibrium constant |
| ϵ | = | Polanyi potential (mol2/KJ2) |
Funding
We would like to acknowledge the Ministry of Human Resource Development, Government of India for financial support.
