Adsorption and desorption kinetics of toxic organic and inorganic ions using an indigenous biomass: Terminalia ivorensis seed waste

Environmental remediation has been a strategy employed by scientists to combat water pollution problems that have led to the scarcity of potable water. Hence, in this study, Terminalia ivorensis seed waste (TISW) was explored for the removal of Congo Red, Methylene Blue, Cadmium and Lead from aqueous solutions. Some experimental variables such as pH, biosorbent dose, initial solute ion concentration, agitation time and temperature were optimised. The surface microstructures of TISW were studied using proximate analysis, bulk density, specific surface area, pH of Point of Zero Charge, Fourier Transform Infra Red Spectroscopy, Thermogravimetric/Differential Thermal Analysis, Scanning Electron Microscopy and Energy Dispersive Analysis of X-ray. The maximum Langmuir monolayer saturation adsorption capacity, qmaxL\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$q_{{\max_{L} }}$$\end{document}, was obtained as 175.44 mg/g for the removal of Methylene Blue by TISW. Also, the qmaxL\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$q_{{\max_{L} }}$$\end{document} for CR, Cd(II) ion and Pb(II) ion were 85.47, 12.58 and 52.97 mg/g, respectively. Also, the pseudo-first-order constant, k1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$k_{{_{1} }}$$\end{document}, and pseudo-second-order rate constant, k2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$k_{2}$$\end{document}, are 0.008–0.026 min−1 and 0.012–0.417 mg g−1 min−1, respectively. Hence, TISW is recommended as a good adsorbent for the removal of both toxic industrial dyes and toxic metal ions from polluted water.


Introduction
The quest for potable water has been a serious challenge to the global ecological balance, especially in developed countries. The recent interest in water shortage and water pollution has driven researchers very hard, so as to look for a lasting, effective and efficient solution to this menace combating the survival of human lives and the ecology. Today, 800 million people still lack access to potable water. For instance, only 46% of the Oceania population and 39% of the Sub-Sahara Africa population have access to potable water [1][2][3][4]. The sporadic rise in human activities over the decades has led to the consistent release of various recalcitrant anthropogenic pollutants into water bodies, thereby causing a sharp drop in the quality of the ecosystem. Eradication of these deleterious pollutants is difficult using classical water purification systems. Report from the World Health Organisation (WHO) showed that 1.8 million people die from polluted water-related diseases [2]. In Nigeria, this problem aggravates the sustainability of its ecology, leading to the precarious survival of flora and fauna. Hence, this has heralded an urgent need for researchers to proffer a sustainable solution to this life quagmire [5][6][7][8]. Toxic metals are known to be the most problematic pollutants, due to their non-biodegradable nature. Irrespective of the huge effort that has been put together by researchers to minimise their environmental impact, toxic metals in the environment still have adverse effects on human, fauna and flora. The toxicological effects of Cd(II) and Pb(II) in humans include bone lesions, cancers (kidney and lung), hypertension, inhibition of haemoglobin formation, sterility, infants brain impairment, learning disabilities, abortion, and kidney damage. To date, various remediation technologies have been used to treat polluted water containing toxic synthetic dyes and metals. These are coagulation, chemical oxidation, photodegradation, aerobic or anaerobic oxidation, precipitation, membrane filtration, dialysis, ion exchange, solvent extraction, reverse osmosis, among others [9,10]. These technologies have some drawbacks, such as low selectivity, incomplete removal, cost ineffectiveness and production of large amount of secondary sludge. Adsorption is known as a green, sustainable and cost-effective technology, which is an alternative to other remediation technologies mentioned above. In recent times, natural or modified biomaterials (biosorbents and agricultural byproducts), which comprise lignin, cellulose, hemicelluloses and other organic compounds that have various functional moieties, have been found to be ubiquitous, easily sourced, cheap, green, sustainable and good adsorbents for clean recovery of toxic synthetic dyes and metals [9]. Some researchers in their previous treatises have used eucalyptus seeds [9], peanut hulls [11], corn cob [12], almond shell, hazelnut shell [13], olive cake [14], mungbean husk [15], mango peel waste [16], orange waste [17], Scolymus hispanicus L. [18], chemically modified orange peel [19], Nauclea diderrichii seed biomass [20,21], Zea mays seed chaff [22], Mesoporous SiO 2 /graphene oxide nanoparticles-modified Nauclea diderrichii seed biomass [23,24], Parkia biglobosa biomass [25], Papaya-clay combo [26], MnO 2 nanoparticles-modified Nauclea diderrichii biomass waste [27], TiO 2 nanoparticlesmodified Nauclea diderrichii seed biomass [28], Pentaclethra macrophylla and Malacantha alnifolia barks [29]. Other researchers in the literature used other adsorbent and techniques to treat wastewaters in addition to adsorption .
Terminalia ivorensis, a timber tree, is the sole member of the genus that occurs naturally in West Africa. It is an indigenous plant (family Combretaceae) which is recognised in the South-western rain forest of Nigeria and Ghana. The bark is used as a lotion for the treatment of wounds, sores and cuts. Terminalia ivorensis is a large deciduous forest tree. On plantations, weeding up to the second year and line cleaning or creeper cutting from the third to sixth year may be necessary. With the diverse native uses of this species, its utility can be further enhanced for agroforestry development by the present research effort on it [54]. Terminalia ivorensis is found in the rainforest but is predominantly a tree of seasonal forest zones. Terminalia ivorensis has numerous uses in the building, construction, carpentry industries and household equipment. Also, this plant can also use as ethnomedicine, a lotion for the treatment of wounds, sores and cuts because it healed without scar [54].
The seed epicarp of Terminalia ivorensis is initially removed before the seed is planted. This seed epicarp constitutes a colossal amount of obnoxious waste. This has informed our choice of exploring this waste as a biosorbent for this research. Conventional remediation technologies like coagulation, membrane filtration, dialysis, reverse osmosis, etc., utilized to treat water polluted with toxic metal ions and dyes are very expensive and result in secondary pollution. The use of Terminalia ivorensis seed waste will avail researchers and industries the opportunity to substitute the aforementioned cocktails of conventional technologies above with very cheap, convenient, suitable, eco-friendly and secondary pollution-free technology to treat polluted water.
This work explores the remediation potential of green, sustainable, cost-effective, ubiquitous, and locally sourced biomass of Terminalia ivorensis seed waste (TISW) for some toxic pollutants studied. To the best of the authors' knowledge, TISW is a new biological adsorbent which is reported to have good uptake capacities for MB, CR, Cd(II) and Pb(II).

Experimental
Preparation of Terminalia ivorensis seed waste (TISW) Terminalia ivorensis seed waste (TISW) was obtained from the Forest Research Institute of Nigeria (FRIN), in Ibadan (7°23 0 16 00 North, 3°53 0 47 00 East), Nigeria. After collection, it was air dried for four weeks and later oven dried for 22 h at 70°C. The dried bark was cut into small pieces and pulverised. Further drying was carried out for 6 h. The pulverised TISW was sieved to 250 lm, put into plastic containers and used for various adsorption experiments.

Surface microstructures of TISW
Proximate analysis, bulk density, pH of point of zero charge (PZC), specific surface area (SSA), Fourier transform infra red spectroscopy (FTIR), thermogravimetric/differential thermal analysis (TG/DTA), scanning electron microscopy (SEM) and energy dispersive analysis of X-ray (EDAX) of TISW Proximate analysis and bulk density of TISW were determined according to the published protocol of Ofomaja and Naidoo [55]. The pH of point zero charge of TISW was determined according to the published protocol of Stumm and Morgan [56]. The specific surface area of TISW was determined according to the published protocol of Sears [57]. The Fourier Transform Infra Red spectroscopic analyses of unloaded, and toxic metals/dyes loaded TISW were carried out by Perkin Elmer FTIR Spectrophotometer (Spectrum Version 2) at the scanning frequencies of 400-4000 cm -1 . The Perkin Elmer thermogravimetric/ differential thermal analysis (TG/DTA) was carried out by Perkin Elmer TG/DTA thermal analyser. Furthermore, the surface microstructures of TISW were carried out by Scanning Electron Microscopy (SEM) instrument, coupled with Energy Dispersive Analysis of X-ray (EDAX), JEOL JSM-6390 LV Model.
All the experimental details and mathematical equations used for these adsorption and desorption studies are shown in the Electronic Supporting Information (ESI) of this manuscript.

Results and discussion
Surface characterization of TISW microstructures Proximate analysis, bulk density, PZC, SSA, FTIR, TG/ DTA, SEM and EDAX of TISW The percentage proximate compositions of TISW on dry weight basis are depicted in Table 1. The determined bulk density of TISW was 0.05 g cm -3 . The SSA of TISW was 240.6 m 2 g -1 . The PZC of the TISW was 6.44.
The PZC or (isoelectric pH) of biosorbent is the pH at which the density of anionic moieties is equal to that of the cationic moieties on a biosorbent surface. At pH \ PZC, the surface of a biosorbent is predominantly cationic, while at pH [ PZC, its surface is predominantly anionic. The functional moieties on TISW surface probably acquire negative or positive charges depending on the solution pH [55]. The PZC result of TISW suggests that it possesses a broad solution pH range to retain its positive charges (see Fig. 1).
The FTIR spectra of TISW, with its loaded CR, MB, Pb 2? and Cd 2? analogues are shown in figures S1a-S1e of the ESI. The free O-H stretch for TISW appeared at 3871 and 3748 cm -1 . After loading TISW with CR, MB and Pb 2? , there was no shift in the vibration frequency of the free O-H stretch. For Cd 2? -loaded TISW, the vibration frequency shifted to 3759 cm -1 . The N-H stretch of TISW was observed at 3456 cm -1 . The N-H stretch for CR, MB, Pb 2? and Cd 2? -loaded TISW shifted to 3445, 3438, 3447 and 3443 cm -1 , respectively. These shifts in the vibration frequencies might be due to binding of these toxic ions onto the functional moieties in the cell walls of TISW [29]. The C-H of CH 2 and CH 3 for TISW was observed at 2935 cm -1 . No significant shift was observed for MB, Pb 2? and Cd 2? -loaded TISW. But for CR-loaded TISW, the C-H vibration frequency decreased to 2924 cm -1 . The -C=O stretch for TISW was found at 1648 cm -1 . For MBloaded TISW, the vibration frequency decreased 1623 cm -1 . There were negligible shifts in the vibration frequency of -C=O stretch for TISW loaded with CR, Pb 2? and Cd 2? . The aromatic -C=C-stretch for TISW appeared at 1544 cm -1 . Also, there was no significant change in the -C=C-vibration frequency when TISW was loaded with CR, MB, Pb 2? and Cd 2? . The C-H bend for TISW appeared at 1359 cm -1 . This vibration frequency increased to 1376 and 1384 cm -1 for CR-loaded TISW, and Pb 2? and Cd 2? -loaded TISW. For MB-loaded TISW, this vibration frequency decreased to 1348 cm -1 . The -C-O bend for TISW was observed at 1057 cm -1 . However, there were negligible shifts in the vibration frequency of -C-O bend for TISW loaded with MB, CR, Pb 2? and Cd 2? . For TISW, the -C-O out of plane deformation bend was observed at 582 cm -1 . This vibration frequency shifted to 571 and 568 cm -1 for CR and MB-loaded TISW, and Pb 2? and Cd 2? -loaded TISW, respectively. The various shifts in the stretch and bend vibration frequencies after loading TISW with the studied pollutant ions/molecules might result from chelation, precipitation and ion exchange reactions that was involved in the biosorption process (see Table 2) [29].
The TG of TISW (see Fig. 2) showed that \220°C, ca. 11% weight loss was observed due to the loss of surface water from TISW. At temperature [220 and \550°C, ca. 55% weight loss was observed, which was assigned to the loss of the volatile components of lignocelluloses and hemicelluloses of TISW [20,21]. Above 550°C, TISW was thermally stable. For DTA (also see Fig. 2) of TISW, exothermic heat flow assigned to 1% decrease in derivative weight was observed from 33 to 150°C, endothermic heat flow assigned to 1.5% increase in derivative weight was observed from [150 to 180°C, another exothermic heat flow assigned to 5% decrease in derivative weight was observed from 180 to 350°C and two endothermic heat flows assigned to 3.5 and 0.5% increases in derivative weight were observed from [350 to 400°C and 400 to 580°C, respectively. The exothermic heat flows led to the dissociation of some chemical bonds of lignocelluloses and hemicelluloses of TISW. Also, the endothermic heat flows led to the association of some chemical bonds to form small molecules such as CO, CO 2 , NH 3 , etc. [20,21,25,58].
The SEM micrographs of TISW show tiny irregular, scattered and spaced fibrils of the lignocelluloses that are contained in the cell walls that comprise lumped particles of unconnected and broken walls. The EDAX of TISW showed the elemental compositions of TISW, which was an indication of the constituents of the functional moieties in TISW (see Fig. 3a-d).

Influence of pH on the removal of sorbate ions onto TISW
The influence of solution pH on the biosorption capacity of TISW largely depends on the speciation of the sorbate or solute ions/molecules at different pHs of the aqueous solutions. The removals of CR and MB onto TISW were highest at pH 2.0 and pH 12.0, respectively. These were obtained as 3.34 and 12.36 mg/g, respectively. The biosorption of CR was optimum at pH 2.0 due to increase in the proton cloud densities of TISW (see Fig. 4). This enabled negatively charged CR molecules to bind easily to the surface of TISW. On the other hand, the removal of MB onto TISW was found to be optimum at pH 12.0 due to the low proton cloud densities on the surface of TISW. This accounted for the increase in the removal of positively charged MB molecules onto TISW [21,29].
Furthermore, the removal of Cd 2? onto TISW was highest at pH 6.0. This was obtained at 10.60 mg/g. Also, [pH 7.0, there was a very slight increase in the removal of Cd 2? to 10.64 mg/g. The negatively charged TISW surface at weak acidic and neutral pH favoured the high uptake of Cd 2? due to deprotonation (low proton density). The very negligible increase for the removal of Cd 2? by TISW observed at [pH 6.0 might be due to the likelihood of the precipitation of Cd 2? on the functional sites on the cell walls of TISW. On the other hand, the removal of Pb 2? by TISW was highest at pH 6.0. This was obtained at 12.13 mg/g. At pH [6.0-7.0, Pb 2? no longer exists in the solution. The speciation of Pb 2? at this pH led  to the formation of Pb(OH) ? , Pb(OH) 2 , Pb(OH) 3 and Pb(OH) 4 2-. From the PZC value of TISW, which was 6.44, it suggested that TISW retained positive charges on its surface over a pH range \6.44. Due to this, TISW would biosorbed high amount of CR molecules than the positive pollutant ions/molecules through ion exchange mechanism and electrostatic attraction. The adsorption of Pb 2? continued until precipitation occurred at pH [6.0. Hence, at pH [6.0-7.0, the binding of Pb(OH) ? species to the TISW biosorbent surface occurred by complexation mechanism and, at this point, further biosorption of Pb 2? ceased. Hence, the main mechanisms by which MB and CR molecules interact with TISW were by electrostatic attraction and p-p hydrophobic interactions. These p-p hydrophobic interactions are higher in CR molecule than MB molecule due to the many aromatic rings in CR thus it has higher propensity to bind to the negatively charged functional moieties on the surface of TISW by p-p hydrophobic interactions than MB. Electrostatic attraction occurred when MB or CR molecules bound to the negatively charged functional moieties on the surface of TISW depending on the pH of the aqueous solutions. On the other hand, the main mechanisms for the uptake of Cd 2? and Pb 2? by TISW were by electrostatic attraction and complexation, which are dependent on the pH of the working solutions as expounded above [29].
Influence of adsorbent dose on the removal of sorbate ions onto TISW The amount of sorbate ions biosorbed decreased with increase in biosorbent dose from 10 to 200 mg. This decrease became more pronounced as the weight of the biosorbent increased, resulting in the agglomeration or aggregation of biosorbent particles, probably blockage of biosorption sites, reduced surface area for sorbate-sorbent interaction and the lengthening of diffusion path [55]. Figure 5 shows the plots of the amount of solute ions adsorbed at equilibrium, q e (mg/ g) against adsorbent dose (mg).

Influence of initial sorbate ions concentration on the biosorption capacity of TISW
The initial sorbate ions concentration is a cogent factor that determines the mass transfer and diffusion dynamics of the biosorption of sorbate or solute ions onto biomasses. Also, increase in the initial sorbate ions concentration is the driving force that is needed to overcome the mass transfer resistance of the uptake of solute ions onto the surface of the biomass [59].
As the initial concentrations of CR and MB increased from 25 to 750 mg/L, there was a commensurate rise in their removal from 6.30 to 362.80 and 10.17 to 362.04 mg/ g respectively. Also, the increase in the initial concentrations of Cd 2? and Pb 2? from 25 to 750 mg/L also amounted in the proportionate increase in Cd 2? and Pb 2? biosorbed by TISW from 11.55 to 146.89 and 10.48 to 176.22 mg/g, respectively. It is noteworthy to mention here that the increase in the initial concentration of sorbate ions led to the corresponding increase in their uptakes, as they occupied the functional moieties on the surface of TISW. The binding of these solute ions to these functional moieties in the active sites occurred in quick successions until they were occupied [25,29].

Influence of agitation time on the removal of sorbate ions onto TISW
The residence time of solute ions plays a salient role in the solute ions uptake onto the biosorbent surface, due to its influence on the sorbent-solute interface. Ho [60] and Onal et al. [61] proposed that biosorption consists of three steps, which are: (a) the diffusion of adsorbate through the solution to the external surface of the adsorbent or the boundary layer The biosorption of CR by TISW at temperature of 300 K increased up to 15 min. Thereafter, equilibrium was attained. Also, the biosorption of CR by TISW increased up to 30 and 60 min at 320 and 340 K respectively, after which equilibrium was reached. It could be said that  increase in temperature led to an increase in the time equilibrium was attained for the biosorption of CR onto TISW. At 300 K, CR molecules rapidly occupied the available functional moieties on the active sites in 15 min of biosorption process. At 320 and 340 K, the available functional moieties on the active sites were occupied at 30 and 60 min, respectively. Although, increase in the temperature from 300 to 340 K was meant to increase in the driving force (mass transfer) of CR molecules onto the functional moieties in the pores of TISW due to the increase in the collision frequency and mobility of CR molecules [29,62]. This temperature increase might have led to the rupture of some chemical bonds of the functional moieties of TISW, distorting the p-p stacking from hydrophobic interactions of CR aromatic rings. Hence, this phenomenon decreased the propensity of CR molecules to bind to TISW surface [29]. The biosorption of MB onto TISW at 300 and 320 K increased up to 60 min. Thereafter, a slight increase in the uptake of MB was observed up to 120 min, after which equilibrium was attained. At 340 K, the biosorption of MB increased up to 120 min, after which equilibrium was reached. Increment in the temperature made MB to exhibit a dissociated form that decreased the rate at which it bound onto the functional moieties in the pores of TISW [29,62]. The biosorption of Cd 2? onto TISW at 300 K increased up to 30 min, respectively, and [30 min of Cd 2? uptake culminated into equilibrium. For the biosorption of Pb 2? by TISW at 320 and 340 K, the uptake of Pb 2? increased up to 15 min, after which equilibrium was observed. The increase in the mass transfer of Pb 2? onto the functional moieties in the TISW pores was due to the fast diffusion of Pb 2? from the solute phase onto the sorbent [61,62].

Equilibrium, kinetics and thermodynamics of CR, MB, Cd 21 and Pb 21 removal by TISW
To know the biosorption capacity of TISW for CR, MB, Cd 2? and Pb 2? , the experimental data were modelled with some equilibrium models. Langmuir isotherm fits the experimental data for the removal of CR, MB, Cd 2? and Pb 2? by TISW better than the Freundlich and Temkin isotherms. The correlation co-efficient values for the Langmuir isotherm were higher than those for Freundlich and Temkin isotherms. The saturation monolayer adsorption capacities, q max L , of TISW for CR, MB, Cd 2? and Pb 2? were 85.47, 175.44, 12.58 and 52.91 mg g -1 , respectively (see Table 3). Lucidly, it is noteworthy to say that the homogeneous nature of TISW surface favoured the uptake of MB molecules more than the other pollutant ions of interest in this work. From Freundlich isotherm, it can be deduced that the values for the biosorption affinity, 1=n, for the uptake of CR, MB, Cd 2? and Pb 2? onto TISW were  Fig. 6a-c. From these nonlinear isotherm plots, it was deduced that the equilibrium data better fit the nonlinear isotherms than the linear isotherms due to the higher correlation coefficient values (R 2 values) obtained for these plots, when compared with those obtained for linear isotherm plots. For the nonlinear isotherm plots, the reduced Chi square values (v 2 values) and the residual sum of squares values indicated that Langmuir isotherm better fits the equilibrium data than Freundlich and Temkin isotherms (see Table 4).
The kinetics of biosorption gives a good idea of how the experimental timing controls the mechanism, chemical reaction and the bulk transfer of the solute ions onto the biosorbent surface. Table 5 indicates that pseudo-secondorder kinetic equation gave better fits to the experimental data than pseudo-first-order kinetic equation for the removal of CR, MB, Cd 2? and Pb 2? by TISW. The correlation co-efficient values for pseudo-second-order kinetic equation were higher than those obtained for pseudo-firstorder kinetic equation at the experimental temperatures. This suggests that the mechanism for the biosorption process is chemisorption. The pseudo-second-order rate constants, k 2 , for the removal of CR, MB, Cd 2? and Pb 2? by TISW at 300-340 K were k 2 0.417 g mg -1 min -1 , while the pseudo-first-order rate constants, k 1 , for the removal of CR, MB, Cd 2? and Pb 2? by TISW at 300-340 K were k 1 0.026 min -1 . The Weber-Morris intraparticle diffusion equation indicated that the plots did not pass through the origin, due to the fact that the values of the boundary film or the thickness of the boundary layer were c ! 0 in all cases. This implies that intraparticle diffusion process was not the only rate controlling or limiting step for the biosorption process, but pore diffusion and film diffusion might have taken place in the rate controlling or limiting step [29,63,64]. The nonlinear plots (pseudo-first-order, pseudo-secondorder and intraparticle diffusion equations) for the removal of CR, MB, Pb 2? and Cd 2? onto TISW are shown in Tables 6 and 7. It was deduced that the kinetic data better fit the nonlinear kinetic equation than the linear kinetic equations. This resulted from the fact that the correlation coefficient values (R 2 values) obtained for these plots were higher than those obtained for the linear kinetic equations. For the nonlinear kinetic plots, the reduced Chi square values (v 2 values) and the residual sum of squares values suggested that pseudo-second-order equations gave better fit to the kinetic data when compared to pseudo-first-order and intraparticle diffusion equations. Figure 7a-c depicts the nonlinear kinetic plots for pseudo-first-order, pseudosecond-order and intraparticle diffusion equations for biosorbed CR, MB, Cd 2? and Pb 2? by TISW. But this work has shown that low-cost TISW demonstrated remediation potential for both toxic industrial dyestuffs and toxic metal ions. Hence, TISW has a wide array of applications for environmental remediation.
From thermodynamic standpoint (see Table 8 Table 9 shows the adsorption capacities, q max L (mg/g) of some adsorbents for CR, MB, Cd 2? and Pb 2? used by researchers as reported in literature.

Conclusion
For the first time, Terminalia ivorensis seed waste (TISW) demonstrated a good potential for the removal of CR, MB, Cd 2? and Pb 2? . Proximate analysis, bulk density, specific surface area, pH of point of zero charge, Fourier transform infra red spectroscopy, scanning electron microscopy, thermogravimetric/differential thermal analysis and energy dispersive analysis of X-ray were used to study the surface texture or morphology of TISW. The equilibrium data best fit the Langmuir isotherm, with a maximum Langmuir monolayer saturation adsorption capacity, q max L = 175.44 mg MB per g of TISW. The kinetic data best fit the pseudo-second-order equation for the removal of CR, MB, Cd 2? and Pb 2? onto TISW. This study revealed that TISW, a benign agricultural seed waste, could  be recommended as ubiquitous and cheap biological adsorbent for environmental remediation of toxic industrial dyestuffs and toxic metals.