Elsevier

Journal of Hazardous Materials

Volume 369, 5 May 2019, Pages 199-213
Journal of Hazardous Materials

Collagenic waste and rubber based resin-cured biocomposite adsorbent for high-performance removal(s) of Hg(II), safranine, and brilliant cresyl blue: A cost-friendly waste management approach

https://doi.org/10.1016/j.jhazmat.2019.02.004Get rights and content

Highlights

  • Unorthodox non-sulfur curing of rubber using collagenic solid waste.

  • Reusable biocomposite via optimum curing for cost-friendly waste management.

  • Advanced adsorbed/unadsorbed microstructural analyses for superadsorption mechanism.

  • 13C NMR, XPS, FTIR, UV–vis, TGA, XRD, and isotherms-kinetics-thermodynamics.

  • Removals of Hg(II) and safranine/brilliant cresyl blue.

Abstract

Goat buffing dust (GBD), an abundantly available collagenic-waste and crosslinked styrene butadiene rubber (SBR)-based scalable biocomposite showing excellent physicochemical properties and reusability was synthesized via systematic optimization of torque and time for exclusion(s) of dyes, such as safranine (SF) and brilliant cresyl blue (BCB), and Hg(II). The GBD-aided non-sulfur curing of SBR was attempted via chromane mechanism-based reaction between resin components of GBD and pendant ̶ C=C ̶ of SBR. The decrease in the relative extent of unsaturation in cured-SBRGBD, alteration of crystallinity, surface properties, elevated thermal stabilities, and ligand-selective superadsorption were inferred through extensive microstructural analyses of unadsorbed and/or adsorbed SBRGBD using 13C NMR, O1s-/N1s-/C1s-/Hg4f7/2,5/2-XPS, FTIR, UV–vis, TGA, XRD, FESEM, and EDX. Interactive effects between pHi, temperature, and concentration on adsorption capacities (ACs) were optimized through response surface methodology (RSM). The ionic interaction between SBRGBD and SF, BCB, and Hg(II) was understood through FTIR analyses, fitting of kinetics data to pseudosecond order model, and activation energies. BET and Langmuir isotherms were fitted the best to BCB and SF/Hg(II), respectively. Thermodynamically spontaneous chemisorption showed the maximum ACs of 165.63, 251.18, and 225.56 mg g−1 for SF, BCB, and Hg(II), respectively, at 100 ppm, 303 K, and adsorbent dose = 0.015 g.

Introduction

Leather industry generates large amounts of collagenic solid wastes, such as trimmings, fleshings, splits, shaving, and goat buffing dust (GBD). About 200 kg finished leather is produced from 1000 kg wet salted hides, accompanied by more than 600 kg solid wastes and byproducts [1,2]. Among the collagenic solid wastes, BD is an important microfine, particulate, and chromium-containing solid waste that is generated substantially during buffing operation conducted on pre-finished leather. GBD causes respiratory tract ailments, ulcers, perforated nasal septum, kidney malfunction, and lung cancer and thus, special disposal technique should be adopted to minimize the harmful effects of GBD. Earlier, several techniques, such as pyrolysis, incineration, and bioremediation, were attempted for effective BD disposal. In the recent past, leather solid wastes have been utilized as filler for fabricating rubber composites based on carboxylated butadiene-acrylonitrile rubber [3], butadiene-acrylonitrile rubber [3,4], nitrile rubber [[5], [6], [7]], neoprene rubber [6], styrene butadiene rubber (SBR) [[6], [7], [8]], and natural rubber [[8], [9], [10]]. The reaction of liquid carboxyl-terminated rubber with triepoxide was catalyzed by the GBD, in which chromium complexes and amino groups of BD acted as catalytic active centres in the reaction of liquid carboxyl-terminated rubber with triepoxide [4]. SBR is non-polar elastomeric synthetic copolymer consisting of styrene and 1,3-butadiene monomers. SBR is widely used as the matrix for rubber composites and nanocomposites because of the suitable mechanical and thermal properties [11,12], excellent abrasion resistance and processability, aging stability, and low-temperature properties [[13], [14], [15], [16]]. Unlike carboxyl-terminated rubber [17], SBR is devoid of carboxyl groups. However, being a copolymer of styrene and butadiene, SBR contains double bonds, which act as the active sites for chromane mechanism-based vulcanization of SBR by phenol-formaldehyde condensates.

GBD contains tanning agents, such as chromium complexes, resoles, urea-formaldehyde-, naphthalene-formaldehyde sulfonic acid-, melamine-formaldehyde-condensates, and polyphenolic compounds of tannins. Among the resoles, bis-phenol-based phenol-formaldehyde condensates are regularly used as synthetic tanning agents in leather manufacturing. Thus, GBD carries significant amounts of bis-phenol-based phenol-formaldehyde condensates bound reversibly with collagen. Accordingly, GBD-based vulcanization should preferably follow the chromane-mechanism instead of allyl hydrogen-mechanism. Accordingly, GBD may function as filler, along with the vulcanizing agent in SBR-composite.

Chemical industries, such as leather, textile, cosmetics, plastic, paper, pharmaceutical, and food, use more than 10,000 synthetic dyes and pigments to attain the desired aesthetic look in finished products. However, around 15 wt. % of such non-biodegradable aromatic dyes is released as waste effluents causing serious pollution to eco-system because of their carcinogenicity, teratogenicity, and mutagenicity. SF is frequently used as colorant of wool, silk, polymer, and leather. SF imparts several harmful effects including carcinogenicity, mitochondrial toxicity, and mutagenicity. BCB helps determine oxalate, nitrite, formaldehyde, hydrazine, protein, and cyclodextrin. Moreover, BCB acts as photoconductor, photocatalyst, and fluorophore. BCB damages DNA via electrostatic attraction and/or intercalation. According to the United States Environmental Protection Agency, the maximum allowable limit of Hg(II) are 10 μg L−1 and 0.002 mg L−1 in waste- and drinking-water, respectively. Therefore, it is tantamount to eliminate even trace amounts of Hg(II) before their discharge into the environment for environmental protection and human safety [[18], [19], [20]]. Mercury causes neurologic malfunction, gastrointestinal disorder, renal problem, and impose detrimental effects on kidneys, lungs, digestive system, nervous system, brain, endocrine system, and reproductive system [21]. Several methods, such as ion-exchange, chemical oxidation, biological treatment, photocatalytic degradation, adsorption [[22], [23], [24]], precipitation [25], membrane-based separation [[26], [27], [28], [29]], ion exchange [30], complexation [31], electro-deposition [32], and reverse osmosis [33], have been employed for water treatment and decontamination. Of these, adsorption is the widely accepted cost-friendly potential technology for water treatment because of the ease of operation and maintenance, cost effectiveness, simplicity of design, high efficiency and performance potential, flexibility, rapidness, and availability of diversified adsorbents [34]. RSM is an empirical statistical technique used for analyzing the synergistic effects of variables on response(s) through execution of the minimum number of runs. RSM effectively reduces the number of runs and thus, facilitates execution of experiments required for construction of the response surface. RSM has been employed for determining the relative effects of several parameters in presence of complex interactions for attaining the maximum AC [[35], [36], [37]]. In the present study, RSM has been employed for systematic optimization of variables for the optimum ACs.

However, utilization of GBD or GBD-based rubber composites as bioadsorbents of dyes and metal ions has not been reported. For the first time, attempts have been made to fabricate stable and recyclable composite bioadsorbent, i.e., SBRGBD, using GBD as non-sulphur curing additive of SBR. Moreover, simultaneous roles of GBD as semisynthetic collagenic bio-filler as well as vulcanizing ingredient have been investigated.

Section snippets

Materials

NaHCO3, Na2B4O7.10H2O, CH3COOH, CH3COONa, KCl, HCl, and NaOH of analytical grades were purchased from Merck. SBR and GBD were collected from TCI (West Bengal, India) and local tannery (Bantala, West Bengal, India), respectively. BCB, SF, and HgCl2 were purchased from Sigma Aldrich.

Synthesis and optimization of the adsorbents

Initially, SBRGBD biocomposites were fabricated in a two-shaft internal roller mixer equipped with the mixing head connected to a Brabender Plasticoder (CDD3000, Germany). The prime objective behind selection of a

13C NMR analyses

13C NMR of SBR showed styrene-specific peaks at 144.01, 131.53, and 129.82 ppm because of aromatic C1, C2/C4/C6, and C3/C5, respectively (Fig. 2a). Moreover, the characteristic peaks at 45.05, 41.98, and 39.92 ppm were attributed to >CH–, –CH2–, and Cα−CH2, respectively. Indeed, varied C = C in backbone and pendent side chain of SBR were incorporated through 1,4- and 1,2-addition of 1,3-butadiene with styrene, respectively. In this context, olefinic C-specific peaks at 129.82/127.52 and

Conclusions

SBRGBD-biocomposite superadsorbent showing very high removal efficiency and recyclability was fabricated through the non-sulphur curing of SBR by novolac-components of waste collagenic solid waste. Chromane mechanism-based curing of SBR was comprehended from the arrival of chromane ring-specific peaks at 3027, 995, 911, and 700 cm–1 in FTIR, along with the substantial decrease in the in peak intensities of olefinic carbons of SBR in NMR, inferred from C1s-/O1s-XPS analyses. Moreover,

Acknowledgements

The authors gratefully acknowledge the Department of Science and Technology (DST), Government of India (YSS/2015/000886), the DST, Government of West Bengal (113(Sanc.)/ST/P/S&T/15G-2/2015), for giving the financial assistance and the Department of Higher Education, Government of West Bengal for giving the opportunity to participate in inter institutional collaboration with the University of Calcutta. M.M. and M.K. are grateful to the University Grants Commission (sr. no. 2061410291, ref no.

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