Removal of Cd(II), Pb(II) and Cr(III) from water using modified residues of Anacardium occidentale L.

Abstract

The pollution of water has been one of the greatest problems faced by the modern society, due to industrialization and urban growth. Rivers, lakes and seas have been continually suffering from the rising concentration of various pollutants, especially toxic elements. This study aimed to evaluate the use of cashew nut shell (Anacardium occidentale) (CNS), after chemical modification with H 2 O 2 , H 2 SO 4 and NaOH, as an new and renewable adsorbent material, for the removal of metals Cd 2+ , Pb 2+ and Cr 3+ in aqueous medium. The adsorbents were characterized by its chemical constitution, structure, infrared spectroscopy, morphology, by means of scanning electron microscopy, determination of the point of zero charge, thermogravimetrical analysis and porosimetry assessments. Tests were conducted to determine the optimal conditions (pH vs. adsorbent mass) for adsorption, by means of multivariate analysis using a central composite design. The adsorption kinetics was evaluated by models of pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion, while adsorption isotherms were linearized by Langmuir, Freundlich and Dubinin-Radushkevich. The effect of initial concentration, temperature and desorption was also performed. The adsorbents exhibited irregular, spongy and heterogeneous structure. FTIR analysis confirms the presence of hydroxyl, aliphatic, phenolic and carboxylic acid groups, which are favorable adsorption characteristics. The pH PZC of adsorbent is 4.35, 2.50 e 6.92, respectively, for CNS H 2 O 2 , H 2 SO 4 and NaOH. The optimum adsorption conditions were as follows: pH 5.0; relation of adsorbent mass/volume of water: 4 g L −1 ; 40 min of contact time for reaching the equilibration. Results suggest the predominance of chemisorption of Cd 2+ and Cr 3+ . Most of biosorbents exhibited good fit by Langmuir and Freundlich, suggesting the occurrence of adsorption on mono-and multilayers. The adsorbents of cashew nut shell exhibited high removal efficiency of Cd, Pb and Cr from waters.

Bioprocessing optimization for efficient simultaneous removal of methylene blue and nickel by Gracilaria seaweed biomass

“… 70 2929 C–H stretching 2932 C–H stretching 3.86 Toteva et al . 72 , Raskó and Kiss 71 2269 N=C=O groups (isocyanate) 2272 –O–C≡N groups 3 Júnior et al 73 2199 C≡N stretching (nitrile group) 72 Ruhland et al 74 2144 C–H stretching in alkanes or alkyne C≡C triple bond stretch 128 Coelho et al 75 ; Zhang et al 76 ; Mamunya and Iurzhenko 77 1648 C=O, C=C stretching 1646 C=O, C=C stretching (amide-I, protein C=O stretching) 2 Shashoua et al . 78 , Sławomir 79 1544 C=C stretching or Amide–II (protein N–H bend, C–N stretch) – – – Ivanova and Kolev 81 , Mallappa and Muniswamy 82 1441 CH 2 –bending vibrations of the methyl group; lipids and proteins) 1436 O–CH 3 methyl esters –5 Drasar and Khripach 83 ; Singh et al 57 1277 C–O stretching 1256 PO asymmetric vibrations (phosphate I) …”

“…It is found that the signal at 2199 cm −1 was assigned to the nitrile group (C≡N) 74 . However, peak at 2144 cm −1 , assigned to the vibrations of hydrocarbons, alkynes (C≡C) non terminal groups 75 . Significantly, the signal at 2144 cm -1 can be assigned to the C-H stretching in alkanes or triple bond stretch of alkyne C≡C 76 .…”

Removal of Pb2+ and Cd2+ From Contaminated Water Using Activated Carbon from Canola Seed Wastes

“…Bands 1760 and 1771 are related to the C=O group, bound to the presence of esters, and bands 720 and 728 are related to CH groupings [21]. In TG ( Figure 2B), two major events are observed, the first one related to water loss (close to 100 °C) [22], an event occurring near 500 °C. Likewise, the observed event at 800 °C is linked to the reactions at 800 are both related to dehydroxylation [23].…”

“…Regarding the kinetic parameters (Table 2), it was possible to verify that the equilibrium occurred at 40 min. According to [22], there is a tendency to deplete the active sites of the adsorbents in the removal of Cd2+ and Pb 2+ . It suggest that times greater than the equilibrium (40 min) are not justified, as this would result in greater time and unnecessary expenses.…”

Enhanced Ibuprofen Adsorption and Desorption on Synthesized Functionalized Magnetic Multiwall Carbon Nanotubes from Aqueous Solution

“…The graph of log ( ) as a function of t gives a straight line for first-order pseudo-adsorption with log q e as the y intercept and (− /2.303) as a slope [ 36 ].…”