Development of low-cost bio-adsorbent from agricultural waste composite for Pb(II) and As(III) sorption from aqueous solution

Figures & data

Figure 1. Flowchart showing summary of the research methodology

Figure 2. FTIR spectrum for carbonized AWC before and after activation

Figure 3. XRD spectra for AWCAC

Figure 4. SEM and EDX analysis on carbonized AWC (a) before (b) after activation

Figure 5. Initial metal ion concentration effect on the adsorption (a) Pb(II) (b) As(III) onto AWCAC at 35°C

Figure 6. Contact time effect on the uptake (a) Pb(II) (b) As(III) onto AWCAC at 35°C

Figure 7. pH effect on Pb(II) and As(III) adsorption by AWCAC (C_o = 150 mg/L, V = 250 mL, W = 0.25 g, shaking speed = 160 rpm, temperature = 35°C, equilibrium time 90 min)

Figure 8. Effect of dosage on Pb(II) and As(III) adsorption by AWCAC (C_o = 150 mg/L, V = 250 mL, W = 0.25 g, shaker speed = 160 rpm, pH = 7, equilibrium time = 90 min, temperature = 35°C)

Figure 9. Temperature effect on the uptake of (a) Pb(II) and (b) As(III) onto AWCAC (V = 250 mL, W = 0.25 g, shaking speed = 160 rpm, pH = 7)

Table 1. Isotherm model parameters for Pb(II) and As(III) adsorption onto AWCAC

		Pb(II)			As(III)
Isotherms	Parameters	35ºC	45ºC	55ºC	35ºC	45ºC	55°C
Langmuir	qm (mg/g)	250.000	166.667	142.857	200.000	145.439	128.730
	KL (L/mg)	1.667	0.950	0.630	1.115	0.750	0.430
	R^2	1.000	0.997	0.994	0.993	0.994	0.995
Freundlich	KF	124.462	110.609	103.544	99.286	77.324	58.616
	1/n	0.159	0.199	0.223	0.427	0.546	0.536
	R^2	0.663	0.513	0.518	0.697	0.795	0.846
Temkin	AT (L/mg)	69.884	53.687	21.250	23.351	7.202	4.338
	B (kJ/mol)	0.176	0.140	0.130	0.075	0.060	0.062
	R^2	0.793	0.657	0.662	0.857	0.890	0.893

Table 2. Monolayer capacity comparison of Pb(II) and As(llI) onto dissimilar adsorbents

Adsorbents	Maximum adsorption Pb(II)	capacities (mg/g) As(III)	References
AWCAC	250	200	Present study
Coconut husk	–	146.30	Kairvelu, Thamaraiselvi, & Namazivayam, (2001)
Rice husk barchar		19.3	Samsuri, Sadegh-Zadeh, & Seh-Bardan, (2013)
Char carbon		89	Pattanayak, Mondal, Mathew, & Lalvani, (2000)
Soyabeans hull	37.37	–	Johns, Marshall, & Toles, (1998)
Iron-chitosan granules	–	2.32	Gupta, Chauhan, & Sankararamakrishnan, (2009)
Peanut shell	35.5	–	Xu & Liu, (2008)
Pecan shell	64.2		Bansode, Losso, Marshall, Rao, & Portier, (2013)
Iron-chitosan flakes		16.2	Gupta et al., (2009)
Ce-Ti oxide adsorbent		6.8	Li, Deng, Yu, Huang, & Lim, (2010)
Palm nut shell	95.2	–	Issabayeva, Arousa, & Sulaiman, (2006)
Rice husk ash	26.11	–	Nnaji, Ebeagwu, & Ugwu, (2017)
Cotton stalk		–	Li, Zheng, Zhang, & Mei, (2010)
Groundnut shell	86.25	–	Isah & Yusuf, (2012)
Hazelnut husk	13.03	–	Imamoglu & Tekir, (2008)
Coconut shell	76.6	–	Kikuchi, Qian, Machida, & Tatsumoto, (2006)

Figure 10. Kinetic plots for pseudo-first-order (a) Pb(II) (b) As(III) onto AWCAC at 35°C

Figure 11. Kinetic plots for pseudo-second-order (a) Pb(II) (b) As(III) onto AWCAC at 35°C

Table 3. Kinetic parameters for Pb(II) and As(III) adsorption onto AWCAC at 35°C

Metals	Metal Conc. (mg/L)	qe,cal (mg/g)	Pseudo-first-order			Pseudo-second-order
			qe, exp(mg/g)	K1(min^−1)	R^2	qe, exp(mg/g)	K2(g/mgmin) (×10^−3)	R^2
Pb(II)	50	42.342	38.860	0.051	0.932	50.761	2.280	0.995
	100	91.343	91.876	0.055	0.965	108.696	0.753	0.996
	150	138.310	141.612	0.047	0.919	158.730	0.044	0.996
As(III)	50	37.634	34.650	0.076	0.952	47.175	2.998	0.988
	100	92.463	82.699	0.033	0.988	97.909	0.472	0.990
	150	133.464	121.479	0.043	0.970	151.330	0.449	0.986

Table 4. Pb(II) and As(III) adsorption onto AWCAC thermodynamic parameters

Metals	ΔH° (kJ/mol)	ΔS° (kJ/mol)	ΔG° (kJ/mol)			R^2
			35ºC	45ºC	55ºC
Pb(II)	− 103.839	−0.272	−18.197	−17.481	−14.766	0.9084
	−73.688	−0.171	−19.422	−19.123	−17.716	0.9670
	−11.036	−0.0026	−10.239	−10.213	−10.187	0.9318
As(III)	−65.899	−0.166	−14.636	−12.972	−11.307	0.9899
	−26.856	−0.0487	−11.859	−11.373	−10.886	0.9998
	−40.990	−0.098	−10.807	−9.827	−8.847	0.9787

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