Introduction

Rapid industrialization and urbanization have resulted in heavy metal contamination of the terrestrial, aerial, and aquatic environments (Ben Salem et al. 2017; Paschoalini et al. 2019; Wang et al. 2018; Yabanli et al. 2014; Yozukmaz et al. 2018). Different industries including battery manufacturing, metallurgy, fertilizers and agrochemical production, and mining are the major environmental contaminators with hazardous heavy metals (Sdiri et al. 2012). Heavy metals are employed in many industrial processes such as galvanizing, electroplating, tanneries, pigment manufacturing, textile manufacturing, paint productions, and metallurgical processes (Järup 2003; Liu et al. 2010).

The heavy metals Pb, Cd, and Cr are highly toxic and are hazardous to health and the environment of biological systems. The maximum permissible limits of Pb, Cd, and Cr in drinkable water, as recommended by WHO, are 0.010 mg/L (Lalhruaitluanga et al. 2010), 0.005 mg/L (Edris et al. 2014), and 0.005 mg/L (Kozlowski and Walkowiak 2002) respectively. Acute intoxication of humans with Pb adversely affects the gastrointestinal system, central nervous system, kidneys, liver and poses many other health problems (Järup 2003). Accumulation of Cd inside humans causes various acute and chronic ailments such as diarrhea, nausea, pulmonary cramps, salivation, skeletal deformation, renal damage (Leyva-Ramos et al. 2005), hypertensions, emphysema, testicular atrophy, sciatica, liver disease (Bedoui et al. 2008), and carcinogenesis (Brown et al. 2000). Chromium concentration exceeding from permissible limit causes respiratory tract irritation, skin and lung carcinoma, epigastric pain, vomiting (Dearwent et al. 2006; Hayes 1988), and many other diseases.

Being biologically non-destructive, heavy metals persist in the environment and, through food chain, cause hazardous effects on both animals’ and plants’ health. To safeguard biological ecosystems and humans from their adverse health problems, the toxic heavy metals must be removed from industrial effluents before being discharged into the water bodies. Various physicochemical techniques, i.e., ion exchange, membrane filtration, chemical precipitation, electro-dialysis adsorption, and extraction, can be employed for heavy metal removal. However, these techniques have their own inherent limitations. Many of these conventional methods require the use of other chemicals and specialized equipment making them costly for use in small industries. Furthermore, concentration of the resulting sludge and its disposal represents an enormous problem.

In contrast, phytoremediation of polluted water using cheap industrial, agricultural, or urban residues is a promising low-cost alternative. Due to its technical feasibility and low cost, biosorptive detoxification of water is superior to other conventional techniques (Davis et al. 2000; Ben Salem et al. 2017; Yabanli et al. 2014; Yozukmaz et al. 2018).

In the current work, chemically modified leaves of Salvia moorcroftiana (CMSML) has been employed as biomass for removal of Pb, Cd, and Cr metals. Metal biosorbing ability of the CMSML was analyzed under various experimental parameters including pH, biosorbent concentration, metal’s initial concentration, temperature, and time. The biosorption kinetics was determined using Langmuir and Freundlich models. Furthermore, thermodynamic parameters and utmost biosorption capacity were also determined and compared with other traditionally used sorbents.

Methods and materials

Materials

The reagents HNO3 (AR 65%), HCl (AR, 38%), and NaOH were purchased from Sigma-Aldrich. The CaCl2 and salts of Pd, Cd, and Cr were purchased from Fluka.

Preparation of biomass and solutions

Leaves of Salvia moorcroftiana were collected from Chinagai, Bajaur Agency, Pakistan. The leaves were washed with deionized water and then initially shade dried at ambient temperature and subsequently in electric oven at 46 °C. Dried leaves were powdered and sieved to obtain particles of 44 mesh size. The powder was first treated with 0.1 M HNO3 for elimination of already contained metals and then with 0.1 M CaCl2·H2O. The chemically treated leaf powder was dried and stored in a desiccator. Stock solutions (1000 ppm) of Pb, Cd, and Cr metals were prepared in deionized water. Working solutions of different concentrations were prepared by diluting appropriate amounts of the stock solution. The pH of working solutions was brought to the desired level using 0.1 M solutions of HCl or NaOH.

Equipment and procedure

All experiments were carried out in temperature-controlled shaker having 16 conical flask clips with an agitation speed of 180 rpm. The effects of various experimental parameters on biosorption were determined through batch biosorption experiments. Each experiment was conducted by treating 100 mL of the test solution with CMSML powder under different conditions of pH (between pH 2.0 and 7.0), biomass dosage (1–30 g/L), metal concentration (20–800 mg/L), time (10–150 min), and temperature (20–50 °C). The CMSML powder was then filtered off with Whatman paper no. 42 and concentrations of the remaining metals in the filtrate were determined by an atomic absorption spectrophotometer. The amount of metals removed by the biosorbent (qe) and the percent biosorptions were calculated using expressions 1 and 2 respectively:

$$ {q}_e=V\times \frac{\left({C}_o-{C}_e\right)}{m} $$
(1)
$$ \%\kern0.5em \mathrm{biosorption}\ \mathrm{yield}=\frac{\left({C}_o-{C}_e\right)}{C_e}\times 100 $$
(2)

where qe adsorption capacity (mg/g) at equilibrium, and Co and Ce are equilibrium initial and final concentrations of metal ions in solution, m is mass of biosorbent used, and V is the volume of test solution.

BJH and BET analysis

Pore size, volume, and surface area were analyzed through BJH and BET analysis using NOVA 2000 e model, Quatachrome, USA. Initially, the samples were degassed at pressure of 133.32 × 10−4 Pa for 6 h and then N2 was adsorbed at 77 K. Total pore volume (Vp) was calculated from volume of nitrogen (as liquid) held at a relative pressure (P/P°) of 0.95.

FT-IR analysis

The FT-IR spectra were recorded at 400–4000 cm−1 using a FT-IR spectrometer (ATI Unicam Mattson 1000). A homogenized mixture of the biomass and KBr (1:9 ratios) was compressed to form KBr pellets of 1 mm thickness.

Adsorption kinetics

Adsorption kinetics study gives information about the adsorption mechanism which is very significant for the biosorption efficiency. Pseudo-first-order and pseudo-second-order kinetic models were applied for investigating the adsorption kinetics. It is important to know the biosorption rate to optimize the parameters (Robinson et al. 2002).

The pseudo-first-order and pseudo-second-order kinetic models were applied using expressions 3 and 4 respectively.

$$ \frac{dqt}{dt}=K1\left(\mathrm{qe}-\mathrm{qt}\right) $$
(3)
$$ \frac{dqt}{dt}=K2\left(\mathrm{qe}-\mathrm{qt}\right)2 $$
(4)

where qt is the adsorption capacity at time t, qe adsorption capacity at equilibrium, and K1 is rate constant (1/min) of pseudo-first-order adsorption. K2 is rate constant (g·min/mg) of pseudo-second-order adsorption.

Adsorption isotherms

Biosorption isotherms explain the interactions between adsorbate molecules and adsorbent surface and therefore Langmuir and Freundlich models were employed (Prasad and Freitas 2000). The Langmuir isotherm model suggests that biosorption is reversible and established only for monolayer on the surface of biosorbent. The isotherm is based on expression 5.

$$ qe=\kern0.5em \frac{qm\ KL\ Ce}{1}+ KLCe $$
(5)

where qe is the mass of the metals biosorbed over adsorbent (mg/g) at equilibrium. Ce is the equilibrium concentration (mg/L), KL (L/mg) is a constant, and qm is maximum mass of metals adsorbed per gram of biosorbent (mg/g), which depends on the number of biosorption sites (Kogej et al. 2010).

The Freundlich equation (expression 6) is an empirical model and is applied for a single solute system to explain the distribution process of solute between solid and aqueous states.

$$ {\mathrm{q}}_{\mathrm{e}}={\mathrm{K}}_{\mathrm{F}}\ {{\mathrm{C}}_{\mathrm{e}}}^{1/n} $$
(6)

where 1/n and KF are Freundlich constant (mg1−1/n L1/n g−1) characteristics of the given adsorbent-adsorbate and the temperature. KF shows the adsorption capacity and n indicates the adsorption energy distribution (Iakovleva and Sillanpää 2013).

Results and discussion

FT-IR analysis

FT-IR spectra of the free and metal loaded CMSML are shown in Fig. 1. The spectrum of unloaded biosorbent (Fig. 1a) indicates the presence of numerous functional groups. The broad peak at 3331.07 cm−1 shows the stretching of –OH group present to aliphatic compounds (Figueira et al. 1999). The intense and strong band at 1053.13 cm−1 is due to C–O stretching indicating the presence of alcoholic groups on biomass surface (Sarı and Tuzen 2008). Absorption peak at 2916.37 cm−1 represents C–H stretching of –CH, –CH2 and –CH3 groups. Absorption peak at 1604.77 cm−1 indicates C=C stretching of aromatic and alkenes (Figueira et al. 1999). The asymmetrical and symmetrical stretching of C–N were respectively observed at 1315.45 cm−1 and 1316.74 cm−1 (Sarı and Tuzen 2008). Absorptions at 1435.04 cm−1 and 1373.32 cm−1 are due to –CH3 and N–H bendings respectively (Tuzen et al. 2009). Most of the functional groups on biosorbent surface have negative charge due to chemical pre-treatment and can effectively bind the metal ions (Figueira et al. 1999).

Fig. 1
figure 1

FT-IR spectra of the biosorbent CMSML (a), biosorbent treated with Pb (II) solution (b), biosorbent treated with Cd (II) solution (c), and biosorbent treated with Cr (VI) solution (d)

Full size image

The FT-IR spectra of CMSML treated with metal solutions showed variation in positions and intensities of some peaks. These variations indicate binding interactions between corresponding functional groups and metals. For CMSML treated with Pb (Fig. 1b), the original peak at 1604.77 cm−1 was shifted to 1622.13 cm−1 showing binding interaction of Pb with C=C group. FT-IR spectrum of CMSML treated with Cd (Fig. 1c) showed slight shifting of the –OH stretching from 3331.07 to 3332.99 cm−1. Treating CMSML with Cd also leads to shifting of –C–H stretching from 2916.37 to 2918.30 cm−1. These changes in absorption frequencies indicate that both the –OH and C–H are involved in the binding of Cd to the biosorbent.

FT-IR spectrum of biosorbent treated with Cr (Fig. 1d) also showed variations in the original absorption frequencies. The peaks located at 3331.07 cm−1, 2916.37 cm−1, and 1604.77 cm−1 were shifted respectively to 3336.85 cm−1, 2918.30 cm−1, and 1633.71 cm−1 indicating metal binding to these functional groups. A new peak in C=O stretching region was observed at 1645.28 cm−1 for CMSML treated with Cr at pH 3.0. This is likely due to oxidation of secondary alcohol to ketone on biosorbent surface by K2Cr2O7. Changes in absorption frequencies affirm binding of the Cr with the –CH, –OH, and C=C groups (Yang and Chen 2008).

Scanning electron microscopy

Surface morphologies of natural and chemically modified Salvia moorcroftiana leaves were characterized by scanning electron microscopy (SEM). The SEM image of natural Salvia moorcroftiana leaves (Fig. 2a) showed a clear morphology. However, after modification and activation, the surface morphology is changed and show irregular edges and crooks (Fig. 2b). The modified surface is appropriate for enhanced metal adsorption (Sarı and Tuzen 2008).

Fig. 2
figure 2

SEM images of Salvia moorcroftiana leaves before modification (a) and after modification with HNO3 and CaCl2 (b)

Full size image

Surface area and pore size analysis

The BET and BJH surface area, pore size, and pore volume were analyzed by surface area and a pore size analyzer. The calculated data are shown in Table 1.

Table 1 Pore volume, average pore diameter, and surface area of CMSML
Full size table

Effect of pH

The ability of hydrogen ions to compete with metal ions for active sites on biomass surface is pH dependent. The effect of altering pH (within pH range 2–7) on biosorption of Pb, Cd, and Cr on CMSML are shown in Fig. 3. The adsorption of Pb and Cd were found to be less at lower pH and was increased with increase in pH. Maximum biosorption of Pb and Cd was observed at pH 6.0 and 7.0 respectively. However, maximum intake of Cr was attained at pH value of 3.0. Biosorption efficiency on different pH conditions can be explained in terms of the availability of functional groups involved binding to metals (Matheickal and Yu 1999).

Fig. 3
figure 3

Effect of pH on biosorption of Pb, Cd, and Cr over CMSML (conditions 100 ppm, 120 min, 0.5 g in 100 mL and 130 rpm)

Full size image

A plausible mechanism for enhanced biosorptive removal of M+2 ions (both Pb (II) and Cd (II)) with increased pH is a substitution of H+ with M+2 on CMSML surface as depicted in expression 7. The driving force for this substitution is the favored coordination between M+2 and ligands present on biosorbent surface at high pH.

$$ {\mathrm{H}}_2{\mathrm{Y}}^{2-}+{\mathrm{M}}^{2+}\rightleftarrows {\mathrm{M}\mathrm{Y}}^{2-}+2{\mathrm{H}}^{+} $$
(7)

At low pH, the release of H+ ions from CMSML surface is not favorable and the coordination of M2+ is limited. However, high pH was also unfavorable for the coordination of M2+ ions because of secondary reaction between M2+ and –OH ions forming MOH+ and M(OH)2 predominate. This leads to decreased concentrations of dissolved metal ions and lower competition for the active sites (Rahman and Sathasivam 2015). Unlike Pd and Cd, the maximum biosorption for Cr (VI) occurred at pH 3.0. At low pH, the Cr is predominately in the form of HCrO4− ions. Maximum biosorption at lower pH is likely to be favored by more H+ ions on the CMSML surface leading to strong attraction between positively charged CMSML surface and chromate ions. When the pH is further lowered (pH < 3), the Cr is predominantly present as H2Cr2O7 having little affinity towards positively charged CMSML surface (Lalhruaitluanga et al. 2010). At pH 6 and above, competitive coordination of both −OH and CrO42− ions with CMSML surface predominates and biosorptions of Cr is not of practical significance (Pagnanelli et al. 2003).

Effect of biosorbent dosage

The effects of biosorbent dosage on biosorption potency are shown in Fig. 4. Percent uptake of all the three metals was observed to increases with biomass loading of up to 5 g/L. For Pb and Cd, the maximum percent biosorptions (99.44% and 99.97% respectively) were attained at biosorbent dosage of 5 g/L and remained persistent at higher dosages. For Cr, drastic increase in % biosorption was observed at dosages up to 5 g/L. Further increase in biosorbent dosage led to a slight increase until the maximum % biosorption (97.99%) was attained at a dosage of 20 g/L. The persistence of % biosorption at higher dosages is due to partial aggregation of biosorbent, decreasing effective surface area for metal biosorption (Barka et al. 2008; Karthikeyan et al. 2007).

Fig. 4
figure 4

Effect of biomass dosage on % biosorptions of Pb (II) at pH 5, Cd (II) at pH 7, and Cr (VI) at pH 3, 100 ppm, 120 min, and 130 rpm

Full size image

Effect of contact time

The influence of contact time on biosorbing capacity as determined is shown in Fig. 5. Contact time was found to affect biosorption capacity of CMSML significantly and the biosorption yield of all the tested metal ions increases with increase in contact time up to 120 min. Biosorption of both Pd and Cd increased significantly for initial contact time of 40 min and negligible increase was observed on further extension of contact time. For Cr, the biosorption capacity kept on increasing until attainment of maximum capacity at 120 min. The optimized time for further experiments was chosen as 120 min (Gong et al. 2005).

Fig. 5
figure 5

Equilibrium contact times for Pb, Cd, and Cr biosorption on CMSML at their respective optimal pH conditions (pH 5 for Pb, pH 7 for Cd ions, and pH 3 for Cr), 100 ppm, biomass 0.5 g in 100 mL, 130 rpm

Full size image

Effect of temperature

The effect of temperatures between 20–50 °C on metal uptake by CMSML is shown in Fig. 6. A decrease in metal uptake was observed with increasing temperature. This is apparently due to damage of the active coordination sites in the biosorbent (Özer and Özer 2003), and due to increasing desorption of the metals from interface into solution (Saltalı et al. 2007). The biosorbent surface has several binding sites and each site can be affected by changing temperature (Aksu and Tezer 2000). For Cd, the biosorption increased up to 40 °C and then acquired decreasing trend on further temperature rise. Uptake of Cr increased up to 30 °C and declined with further rise in temperature. Maximum uptake of Pd and Cd took place at 40 °C while that of Cr at 30 °C.

Fig. 6
figure 6

Effect of temperature on biosorptive removal of Pb, Cd, and Cr over CMSML under optimal conditions of pH and contact times

Full size image

Effect of initial metal ion concentration

Biosorption as a function of metal concentrations was determined by varying initial concentrations of Pb, Cd, and Cr between 20 and 800 mg/L (Fig. 7). The results indicated that by raising the metal concentration, the capability of biosorbent to eliminate the metals increased but percent biosorption was decreased. Although, at higher concentrations, the number of metal ions is more than the available binding sites; however, intraparticle diffusion of the ions on biomass surface leads to a decrease in percent biosorption (Azizi et al. 2016).

Fig. 7
figure 7

Effect of tested metal concentrations on biosorption over CMSML under their respective optimal conditions of pH, dosage, and time

Full size image

Biosorption isotherm models

The Langmuir and Freundlich isotherm models were applied to investigate the probable mechanism of metal biosorption to the CMSML. The Langmuir model predicts monolayer biosorption on homogenous surface having no interaction with biosorbed molecules. However, the model also explains uniform energies of biosorption on the surface and no transmigration of the adsorbate. Langmuir equation is given as (Langmuir 1918)

$$ \frac{Ce}{qe}=\kern0.5em \frac{Ce}{qm}+\frac{1}{KL\ qm} $$
(8)

where qe is the equilibrium concentration of metal ions onto biomass (mg/g), Ce is the equilibrium of metals in solution (mg/L), qm is the biosorption monolayer capability of the biomass (mg/g), and KL is Langmuir constant (L/mg).

A linear relationship was depicted between ratio of Ce/qe and concentrations of metals in solution (Fig. 8). The regression correlation coefficients (R2) showing metal uptake onto CMSML properly followed the Langmuir model. Generally, the isotherm plot indicated enhancement of the biosorption capacity with initial concentration of metal until the surface of CMSML reached saturation. Maximum biosorption potencies (qm) of CMSML were determined to be 136.99 mg/g for Pb, 112.36 mg/g for Cd, and 90.91 mg/g for Cr. The KL(b) values for Pb, Cd, and Cr ions were found to be 0.258 L/mg, 0.0813 L/mg, and 0.028 L/mg respectively. The Freundlich isotherm model, expression 9, explains a monolayer biosorption with a heterogeneous distribution of energetic active sites and strong interactions between biosorbed substances (Freundlich 1907).

$$ \log qe=\log KF+\frac{1}{n}\log Ce $$
(9)

wherein Kf is Freundlich constant of biosorption potential and 1/n is a characteristic empirical parameter relevant to the intensity of biosorption. The Freundlich isotherm plots for biosorptive removal of Pb, Cr, and Cr over CMSML are shown in Fig. 9. The KF and 1/n values calculated for Pb (II), Cd (II), and Cr (IV) were found to be 25.62 and 2.36, 18.47 and 2.97, and 3.64 and 1.57 respectively. The values of 1/n vary from 0 to 1 demonstrating favorable biosorption of all metal ions. The R2 values calculated for Pb, Cd, and Cr were 0.998, 0.988, and 0.933 respectively (Table 2).

Fig. 8
figure 8

Langmuir plots for biosorption of Pd, Cd, and Cr metal ions

Full size image
Fig. 9
figure 9

Freundlich plots for biosorption of Pd, Cd, and Cr metal ions

Full size image
Table 2 Adsorption isotherm constants for CMSML-mediated biosorptive removal of Pd, Cd, and Cr ions
Full size table

A comparison of the biosorption capacity of CMSML with other reported biosorbents for the removal of Pd, Cd, and Cr ions is given in Table 3. CMSML possess higher biosorption capacity than majority of the reported biosorbents suggesting CMSML to be a superior biosorbent for water detoxification.

Table 3 Comparison of biosorption capacity (mg/g) of CMSML with other reported biosorbents for the removal of Pb, Cd, and Cr
Full size table

Biosorption kinetics

To determine the kinetics of CMSML-mediated biosorptive removal of Pd, Cd, and Cr, pseudo-first-order and pseudo-second-order kinetic models were plotted to the findings. Linear rate equation for the pseudo-first-order of Langergren is given (Lagergren 1898).

$$ \ln\ \left({\mathrm{q}}_{\mathrm{e}}-{\mathrm{q}}_{\mathrm{t}}\right)=\ln\ {\mathrm{q}}_{\mathrm{e}}-{\mathrm{K}}_1\mathrm{t} $$
(10)

where qt and qe are the biosorption capabilities (mg/g) at time t and at equilibrium and k1 is the kinetic rate constant. The kinetic rate constant can be explained experimentally by plotting ln (qe − qt) versus t for pseudo-first-order equation as given in Fig. 10. The determination of regression correlation coefficients R2 is low, as shown in Table 4. From the values of R2, it can be deduced that the biosorption of all the three metals do not follow the pseudo-first-order kinetic model (Sari et al. 2008). The findings were also evaluated by pseudo-second-order kinetic model using Eq. 11. (Ho and McKay 1999)

$$ \frac{1}{qt}=\frac{1}{K2\ qe2}+\left(\ \frac{1}{qe}\ \right)t $$
(11)

where K2 (g·mg−1 min−1) is the rate constant for pseudo-second-order process, qt (mg/g) is the biosorption mass at time t, and qe is the biosorbed amount (mg/g) at equilibrium. This kinetic model is likely to point out kinetic behavior of biosorption of heavy metals with chemical sorption being the controlling step of reaction rate (Ho and McKay 2000). The linear plots of the ratio (t/qt) versus t for the pseudo-second-order kinetic model at 20 to 50 °C are presented in Fig. 11. The rate constants K2, the value of R2, and the values of qe are presented in Table 4. The regression correlation coefficient R2 values were very large for the biosorption of the tested metals. The biosorptions of Pb (II), Cd (II), and Cr (IV) ions onto CMSML were found to be well in compliance with the pseudo-second-order kinetic model (Farhan et al. 2013).

Fig. 10
figure 10

Plots obtained for metal biosorptions after applying pseudo-first-order kinetic model

Full size image
Table 4 Kinetic parameters obtained from pseudo-first-order and pseudo-second-order kinetic models for biosorption of Pb, Cd, and Cr onto CMSML
Full size table
Fig. 11
figure 11

Plots obtained for metal biosorptions after applying pseudo-second-order kinetic model

Full size image

Thermodynamic aspects

Thermodynamic parameters including standard enthalpy changes (∆H°), standard change in Gibbs free energy (∆Go°), and standard changes in entropy (∆S°) for biosorptive removal of test metals through CMSML were determined using Eqs. 12 and 13.

$$ {\Delta \mathrm{G}}^{{}^{\circ}}=-\mathrm{RT}\ \ln\ {\mathrm{K}}_{\mathrm{D}} $$
(12)

where R is the universal gas constant, KD (qe/Ce) is the distribution coefficient, and T is temperature in Kelvin (Sawalha et al. 2006). The standard enthalpies (H°) and entropies (S°) were calculated using the following equation:

$$ \mathrm{lnKD}=\frac{\Delta S0}{R}-\frac{\Delta H0}{RT} $$
(13)

The parameters S° and H° were deduced from the intercept and slope of the plot of ln KD vs 1/T yields, respectively and were shown in Fig. 12. The negative ∆G° values calculated for metal uptake in Table 5 show biosorptive removal of the tested metals to be spontaneous and thermodynamically feasible. The negative ∆H° for biosorptions of all the three tested metals indicates the process to be exothermic at 298–323 K. The positive values of ∆S0 indicate that biosorptions were favorable (Singh et al. 2006).

Fig. 12
figure 12

Van’t Hoff’s plot for CMSML-mediated biosorptive uptake of Pd, Cd, and Cr

Full size image
Table 5 Thermodynamic parameters for biosorption of Pd, Cd, and Cr
Full size table

Conclusions

Current study explored different experimental, kinetic, and thermodynamic aspects of the use of chemically modified Salvia moorcroftiana leaves (CMSML) for biosorptive detoxification of aqueous solutions by removing Pb (II), Cd (II), and Cr (IV) ions. The batch biosorption parameters were shown to affect the biosorption potency of CMSML. Biosorption potencies of CMSML for Pb (II), Cd (II), and Cr (IV) ions were 270.27 mg g−1, 100 mg g−1, and 93.90 mg g−1 respectively. FT-IR spectra indicated changes in absorption frequencies of different groups due to metal-ligand binding. At biomass dosage of 5 g, optimum conditions for effective elimination of Pb (II), Cd (II), and Cr (IV) are pH 6.0, 7.0, and 3.0, contact time 120 min, 60 min, and 120 min, temperature 40 °C, 40 °C, and 30 °C, respectively. Kinetic studies indicated that the removal of Pb (II), Cd (II), and Cr (IV) ions onto CMSML obeys the pseudo-second-order kinetics. Thermodynamic studies revealed that the biosorptions of both Pb (II) and Cd (II) ions are spontaneous and exothermic, while that of Cr (IV) ions are endothermic and non-spontaneous. Due to its high biosorption potency and low cost, Salvia moorcroftiana can be considered good alternative to other biosorbents for detoxification of water contaminated with Pb (II), Cd (II), and Cr (IV) ions.