3.4. Analytical figures of merit

sites (L/mg), and qmax is the maximum amount of arsenic per unit weight of adsorbent for

where Ce is the equilibrium concentration (mg/L), qe is the amount of arsenic adsorbed onto the solid phase (mg/g), Kf is an indicator of the adsorption capacity, and n is the heterogeneity

The results in Figure 5(a and b) and Table 1 showed that the correlation coefficient for linear

fitted in Langmuir model, and this signified that the adsorbent had high affinity for arsenic(III)

Figure 5. (a) Langmuir isotherm displaying the adsorption of AsIII onto the surface of the avocado seed by plotting Ce/qe against equilibrium concentration (Ce). (b) Freundlich isotherm showing the adsorption of AsIII onto the surface of the

avocado seed by plotting ln Ce against equilibrium concentration ln qe.

, 0.97) was higher than the Freundlich model (R2

1

<sup>n</sup> log Ce (4)

, 0.72). The data was best

Logqe ¼ logKf þ

complete monolayer coverage.

32 Arsenic - Analytical and Toxicological Studies

factor.

Langmuir model (R2

Freundlich equation is represented as shown in Eq. (4):

Analytical figures of merit for the quantitative analysis of arsenic(III) such as limit of detection (LOD), limit of quantification (LOQ), correlation coefficient (R<sup>2</sup> ), and the relative standard deviation (RSD) were calculated. In order to determine the LOD, the blank solution was subjected to the optimum experimental conditions, and the signals for ten blank samples were measured (n = 10). The limit of detection (LOD), calculated based on 3S/m (where S is the standard deviation of the blank and m is the slope of the calibration curve) was 0.10 mg L�<sup>1</sup> . The limit of quantification (LOQ = 10S/m) was 0.20 mg L�<sup>1</sup> for arsenic(III). The linear calibration curve was plotted with a correlation coefficient of 0.98.

The precision (repeatability) of the batch adsorption method was studied by measurements of eight replicates of 2.0 mg L�<sup>1</sup> standard solution of AsIII as shown in Table 2. The precision, expressed in terms of standard deviation (%RSD), was 2.1.

#### 3.5. Application of the avocado seed adsorbent in real water samples

A water sample from East London municipality was adsorbed by the raw avocado seed under the optimized conditions. It is shown in Figure 6(a and b) that the bio-adsorbent is removed (54 and 55%) from sampling area A and B, respectively. During the adsorption of AsIII from environmental water samples, an interference can be experienced from metal ions such as FeIII, FeII, ZnII, CdII, NiII, MnII, AlIII, PbII, and CuII [10].

This indicated that avocado seed has the great potential in removing heavy metals like AsIII in environmental water samples without being modified.


Table 1. Adsorption isotherms for AsIII adsorption by a bio-adsorbent.


4. Conclusions

Acknowledgements

South Africa.

Author details

References

27:170-175

2 mg L<sup>1</sup>

This work focused on removal of arsenic from aqueous solution using a powdered raw avocado seed. Important parameters that affect adsorption were optimized accordingly, pH 6, analyte

room temperature of 40C. It was observed that raw avocado fruit seed can remove more than 50% of arsenic(III) from real water sample without any modification. The advantages of this bioadsorbent is that it requires less preparation time and is readily available. The use of avocado seeds as a bio-adsorbent will also reduce the waste that is normally discarded in the streets, and it does not affect the food security issues since it is not edible. Due to the advantages that it possesses, it is strongly recommended that it should be incorporated in the removal of toxic heavy metals such as AsIII. The adsorption isotherm data were tested for both Langmuir and Freundlich models. The regression coefficient and RL values, best fitted Langmuir model (R2 = 0.97), and the adsorption capacity was 93.75 mg/g. The Langmuir model means that chemisorption took place at the monolayer of the bio-adsorbent due to the availability of func-

tional groups such as carboxylic acids that have high affinity for metal ions such AsIII.

Khathutshelo Catherine Mqehe-Nedzivhe, Khathutshelo Makhado,

Philiswa Nosizo Nomngongo and Nonhlangabezo Mabuba\*

\*Address all correspondence to: nmabuba@uj.ac.za

University of Johannesburg, Johannesburg, South Africa

Oluwasayo Folasayo Olorundare, Omotayo Ademola Arotiba, Elizabeth Makhatha,

[1] James KA, Meliker JR, Nriagu JO. Arsenic. In: Quah SR, Cockerham WC, editors. The International Encyclopedia of Public Health, 2nd ed. vol. 1. Oxford: Academic Press; 2016;

This work was supported by the National Research Foundation of South Africa (Thuthuka Grant No. 107066 and CPRR Grant No. 98887); the Centre for Nanomaterials Science Research; the National Nanoscience Postgraduate Teaching and Training Platform; the University of Johannesburg (UJ), South Africa; and the Faculty of Science, University of Johannesburg (UJ),

, dosage mass 0.8 g, and contact time 120 min, and temperature was constant from

Bio-adsorbents for the Removal of Heavy Metals from Water

http://dx.doi.org/10.5772/intechopen.73570

35

Table 2. The repeatability of AsIII concentration during the adsorption by avocado seed obtained from a local shop in Johannesburg.

Figure 6. The determination of the percentage (%) of AsIII removed by the bio-adsorbent from (a) Sample A to (b) Sample B using ICPOES.
