Heavy metals are naturally occurring elements that have a high atomic weight and a density at least 5 times greater than that of water. Their multiple industrial, domestic, agricultural, medical and technological applications have led to their wide distribution in the environment; raising concerns over their potential effects on human health and the environment [ 1]. Their toxicity depends on several factors including the dose, route of exposure, and chemical species, as well as the age, gender, genetics, and nutritional status of exposed individuals. Because of their high degree of toxicity, arsenic, cadmium, chromium, lead, and mercury rank among the priority metals that are of public health significance [ 2]. These metallic elements are considered systemic toxicants that are known to induce multiple organ damage, even at lower levels of exposure. They are also classified as human carcinogens (known or probable) according to the U.S. Environmental Protection Agency, and the International Agency for Research on Cancer [ 3]. This review provides an analysis of their environmental occurrence, production and use, potential for human exposure, and molecular mechanisms of toxicity, genotoxicity, and carcinogenicity [ 4].

The aim of this research is to prepare and characterize new adsorbent from biomass Mangiferaindicaleaf using AAS and FT-IR analysis in order to removed Ni(II), Pb(II) and Cu(II) ions from aqueous solution.

Heavy metals are among the most investigated environmental pollutants. Almost any heavy metal and metalloid may be potentially toxic to biota depending upon the dose and duration of exposure. Many elements are classified into the category of heavy metals, but some are relevant in the environmental context [ 5]. List of the environmentally relevant most toxic heavy metals and metalloids contains Cr, Ni, Cu, Zn, Cd, Pb, Hg, and As [ 2]. Heavy metal pollutants most common in the environment are Cr, Mn, Ni, Cu, Zn, Cd, and Pb [ 6], China has suggested four metals, i.e., Cr, Cd, Pb, Hg, and the metalloid As, as the highest priority pollutants for control in the “12^th 5-year plan for comprehensive prevention and control of heavy metal pollution. Some other heavy metals are also hazardous to living organisms depending upon dose and duration of exposure [ 7]. Now days, the contamination of water resources by heavy metals has result serious health issues. Heavy metals in their elemental as well as chemically combined form are toxic, non-degradable and persistence in nature. The presence of heavy metal in aquatic environment is major health concern due to their hazardous nature since they can cause severe health problem for both animal and human being [ 8].

Hence there is need to develop a simple, efficient, inexpensive and economical method for removing dissolved heavy metals from waste water.

The main material used in this research is Mangiferaindica (mango) leaf biomass. Pb(NO₃)₂, Ni(NO₃)₂.6H₂O, CuSO₄.5H₂O, NaOH and HNO₃ were used as received. All solutions were prepared in de-ionized water prepared using a water purification system.

The leaves of Mangiferaindica (mango) was use for this research work. The leaf was collected within the Gombe state university in Gombe, Nigeria. The leaves biomass was washed with tap water to remove dirtied and other particulate matter and rinsed with distilled water. The sample leaves was oven dry at about 120^ᵒC for 24 hrs. The dried leaves was graded and then sieved to uniform the particles (140m). The prepared absorbent was stored in clean air-tight glass bottle until the time of usage. 1000g/L stock solution of Pb(NO₃)_2, Ni(NO₃)₂.6H₂O and CuSO₄.5H₂O were prepared according to standard procedure by dissolving 1.5980g, 4.9530g and 3.935g each in 1L distilled water and serial dilution method from the stock solution to obtain different concentration and atomic absorption spectroscopy(AAS) was used to measure the solutions which was used for further experiments.

The adsorbent surface functional group loaded with adsorbent and unloaded was identified with Fourier Transform Infrared (FTIR) spectroscopy, KBr was used as background material.

The effect of initial metal concentration adsorption of Pb²⁺, Ni²⁺ and Cu²⁺ ions on Mangiferaindicawas determined at different concentration of 10ppm, 15ppm, 20ppm, 35ppm, and 40ppm keeping the pH at 6, room temperature(~25^ᵒC). 50ml solution of pb²⁺, Ni²⁺ and Cu²⁺ ions were transferred into 100ml conical flask, 0.6g of Mangiferaindica sample were added and the solution was shaken for 40min at 150rpm. The solutions were filtered using whatman No1 filter paper and the filtrate was analyzed with AAS (Buck of scientific 205).

The effect of pH on the process of adsorption pb²⁺, Ni²⁺ and Cu²⁺ ions with Mangiferaindicawas determined at different pH value of 2, 4, 6, 8, and 10 optimum initial concentration of metal ions of 15ppm pb, 40ppm Ni and 40ppm Cu at room temperature (~25^ᵒC). 50ml solution of pb²⁺, Ni²⁺ and Cu²⁺ ions were transferred into 100ml conical flask, 0.6g of Mangiferaindica samples were added and the solutions was shaken for 40min at 150rpm. The solutions were filtered using whatman No1 filter paper and the filtrate was analyzed with AAS (Buck of scientific 205).

Effect of adsorbent dose pb²⁺, Ni²⁺ and Cu²⁺ ions with Mangiferaindicawas determined at different amount of dosage of 0.2, 0.4, 0.6, 0.8, and 1.0g under optimum initial concentration of metal ions of 15ppm Pb²⁺, 40ppm Ni²⁺ and 40ppm Cu, pH of 4 pb²⁺, 10 Ni²⁺ and 4 Cu²⁺was suspended in 50ml of pb²⁺, Ni²⁺ and Cu²⁺ ions at room temperature (~25^ᵒC). The pb²⁺, Ni²⁺ and Cu²⁺ ions were transferred into 100ml conical flask, and left to shake for 40min at 150rpm. The solutions were filtered using whatman No1 filter paper and the filtrate was analyzed with AAS (Buck of scientific 205).

Effect of contact time on the adsorption process of pb²⁺, Ni²⁺ and Cu²⁺ ions by Mangiferaindicawas studied at the following time intervals 20, 40, 60, 80, and 100mins at optimum concentration of 15ppm Pb, 40ppm Ni and 40ppm Cu pH of 4 Pb, 10 Ni and Cu, pH of 4 Pb, 10 Ni and 4 Cu, adsorbent dose 0.4 Pb, 0.2 Ni and 0.8 Cu, at room temperature (~25^ᵒC). 50ml of solution pb²⁺, Ni²⁺ and Cu²⁺ ions were transferred into 100ml conical flasks. The solutions were shaken at 150rpm at different time intervals. The solutions were filtered using whatman No1 filter paper and the filtrate was analyzed with AAS (Buck of scientific 205).

Effect of temperature on the adsorption process of pb²⁺, Ni²⁺ and Cu²⁺ ions was studied at the following temperature 25, 35, 45, 55 and 65^ᵒC at the optimum pH of 4 pb²⁺, 10 Ni²⁺ and 4 Cu²⁺, were transferred into 100ml conical flasks, 0.4 pb²⁺, 0.2 Ni²⁺ and 0.8 Cu²⁺, adsorbent was added to pb²⁺, Ni²⁺ and Cu²⁺. The solutions were shaken at 150rpm at different temperatures, contact time of 100min for pb²⁺, Ni²⁺ for 20min and 60min Cu²⁺. The solutions were filtered using whatman No1 filter paper and the filtrate was analyzed with AAS (Buck of scientific 205).

Calculation of metal uptake: metal uptake by Mangiferaindicawas was calculated using the mass balance equation which is shown in

Where q is the metal uptake (mg metal g^-1 dry weight); v (L) is the volume of metal solution contacted with adsorbent: Co is the initial concentration of metal in solution (mg L^-1): Ce is the final concentration of metal in solution (mg L^-1): S in the dry weight (g) of biosorbent used.

In order to ascertain the functional group that are responsible for the adsorption of the metals ions in this study and possibly to explain the mechanism of the adsorption, FT-IR study was carried out on the unloaded and the metal loaded adsorbent ta the optimum pH. The FT-IR spectrum (Figure 1) of unloaded biomass shows a number of distinct absorption bands indicating the complex nature of the leaves. Several distinct and adsorption around 3421 cm^-1 are indicative of O-H groups. Weak bands around 2920cm^-1 in both indicate presence of C-H stretch of alkane. The absorption bands around 1633cm^-1 in the spectra indicate the presence of C=C stretch while the bands around 1450 and 1384 cm^-1 could be attributed to CH₂-CH₂ and CH₂-CH₃ bending bands. Band around 1080cm^-1 could be due to C-O stretch. [ 1]. have reported similar band in loaded and unloaded hust of Oryza sativa shows the characteristic absorption band at 3,400–3,200cm^–1 is assigned for surface O–H stretching whereas C–H stretching had a broad band at 2,921–2,851cm^–1. Moreover, the peak at 1074.0 cm^–1 corresponds to anti-symmetric stretching vibration of Si–O, whereas at 476.2cm^–1 representing the bending vibration of Si–O–Si bond.

Using the metal ions as case of study comparing (Figure 2,Figure 3 andFigure 4) the spectra of Pb²⁺, Ni²⁺ and Cu²⁺ ions loaded biomass with that of the unloaded, it is observed that the band at 3457, 4359 and 3477cm^-1 broadens and its intensity is reduced and the band shift to a higher wave number after metal adsorption. Also the band at 1632cm¹ became slight intense. An ion-exchange process occurred when the metal in the solution was transferred from solution to adsorbent leading to the formation of chemical band.

The amount of Ni²⁺, Pb²⁺ and Cu²⁺ ions adsorbed by Mangiferaindica leaf at equilibrium (qe).Figure 5 indicate the Ni²⁺ ions removal efficiency increased from 65.03 to 75.92% at the concentration of 10 to 40ppm after which the optimum was reached. This shows the optimum adsorption capacity of 2.53mg/g at the concentration 40ppm for nickel (II), lead(II) the percentage removal increased from 98.35 to 99.35% at the concentration of 10 to 40ppm with the optimum adsorption capacity at 3.27mg/g at the concentration 10ppm for lead(II). And the percentage removal of copper (II) ions increase from 67.52 to 78.25% at the concentration of 10 to 40ppm which shows that the optimum adsorption capacity is 2.60mg/g at the concentration 40ppm for copper(II) [ 9].

The effect on the adsorption capacity of Mangiferaindica leaf was investigate on Ni²⁺, Pb²⁺, and Cu²⁺ ions at different pH value of 2, 4, 6, 8 and 10 at optimum concentration of metal ion nickel(II) 40ppm, lead(II) 10ppm and copper(II) 40ppm, at a fixed adsorbent dose 0.6g, contact time of 40mins and temperature 25^oC.

Low percentage of adsorption was observed at pH 2 for Ni²⁺and Pb²⁺, pH 8 Cu²⁺ ions. The optimum percentage adsorption was observed at pH 10 for Ni²⁺ with percentage adsorption of 76.49%, pH 8 for Pb²⁺ with percentage adsorption of 99.11% and pH 4 for Cu²⁺ ions with percentage adsorption of 86.02% as shown inFigure 6. The adsorption of metal ions dependent of pH, adsorption of heavy metal from aqueous solutions depends on the properties of adsorbent and molecule of adsorbate transfer from the solution to the solid phase (Adebayo et al., 2012). It has also being observed that the capacities for the heavy metals are depending on pH. The result shows that high pH favor Ni²⁺ and Pb²⁺ as compare with copper by Mangiferaindica leaf.

At very high pH, the metal ions get precipitated due to hydroxide anion forming a metal hydroxide precipitates for this reason; the optimum pH value was selected to be 6.0 for other subsequent experiment carried out [ 7].

The influence of adsorbent dose on the adsorption capacity of Mangiferaindica leaves was to investigated on Ni²⁺, Pb²⁺, and Cu²⁺ ions by varying the adsorbent dosage of 0.2, 0.4, 0.6, 0.8 and 1.0g. optimum condition of metal concentration of 40ppm for Ni²⁺ and Cu²⁺ and 10ppm for Pb²⁺, pH of 10 for Ni²⁺ pH of 8 for Cu²⁺ pH of 4 for Cu²⁺, agitation time for 40mins at a temperature 25^oC. The result shows that the percentage removal decrease with the increase in amount of adsorbent dose in case of Ni²⁺ and Pb²⁺, but Cu²⁺ percentage removal increase with increase in amount of adsorbent dose. The percentage adsorption of increase from 97.72 to 99.53% at optimum dose 0.2g for Ni²⁺, 98.53 to 98.94% at optimum dose 0.2g for Pb²⁺ and 89.23 to 90.97% at optimum dose 1.0g for Cu²⁺ as shown inFigure 7.

Decreased with increase in adsorbent dosage, this result attributed to the metal ions can easily access the adsorption sites when the adsorbent amount is small. With increasing adsorbent content, the corresponding increase in adsorption per unit mass is less because the metal ions find it difficult to approach the adsorption sites due to overcrowding of adsorbent termed as a kind of solid concentration effect [ 1].

The influence of adsorbent dose on the adsorption capacity of Mangiferaindica leaves was to investigated on Ni²⁺, Pb²⁺, and Cu²⁺ ions by varying the adsorbent dosage of 0.2, 0.4, 0.6, 0.8 and 1.0g. optimum condition of metal concentration of 40ppm for Ni²⁺ and Cu²⁺ and 10ppm for Pb²⁺, pH of 10 for Ni²⁺ pH of 8 for Cu²⁺ pH of 4 for Cu²⁺, agitation time for 40mins at a temperature 25^oC. The result shows that the percentage removal decrease with the increase in amount of adsorbent dose in case of Ni²⁺ and Pb²⁺, but Cu²⁺ percentage removal increase with increase in amount of adsorbent dose. The percentage adsorption of increase from 97.72 to 99.53% at optimum dose 0.2g for Ni²⁺, 98.53 to 98.94% at optimum dose 0.2g for Pb²⁺ and 89.23 to 90.97% at optimum dose 1.0g for Cu²⁺ as shown inFigure 8.

Decreased with increase in adsorbent dosage, this result attributed to the metal ions can easily access the adsorption sites when the adsorbent amount is small. With increasing adsorbent content, the corresponding increase in adsorption per unit mass is less because the metal ions find it difficult to approach the adsorption sites due to overcrowding of adsorbent termed as a kind of solid concentration effect [ 10].

The effect of agitation time on adsorption capacity of Mangiferaindicaleaf was investigate on Ni²⁺, Pb²⁺, and Cu²⁺ ions solution at different contact time of 20, 40, 60 100 and 120min at optimum conditions of metal concentration of 40ppm for Ni²⁺ and Cu²⁺, 10ppm for Pb²⁺, pH of 10 for Ni²⁺ pH of 8 for Cu²⁺ pH of 4 for Cu²⁺, adsorbent of dose 0.2g Ni²⁺ and Pb²⁺, 1.0g for Cu²⁺, at temperature of 25^oC. The result that was observed in Figure: 9, show that the percentage removal all metal ions increase with increase in contact time, until it reaches equilibrium contact time 100min, from 100min to 120min on increase in adsorption that was observed. The percentage adsorption increase from 88.24 to 90.84% for nickel, 99.58 to 99.96% for lead and 87.92 to 90.15% for copper, all at equilibrium time 100min. In the early stage of adsorption more number of vacant sites is available for adsorption to proceed. As constant time increases the adsorption capacity increase until it reaches optimum, the maximum number of sites that got adsorbed to the metal ions increase which becomes difficult for the lead (II) ions to search for the very few remaining sites, thus rate of adsorption remain constant as agitation [ 9].

The equilibrium uptake of Ni²⁺, Pb²⁺, and Cu²⁺ ions by Mangiferaindica leaf was determined at different temperature of 25, 35, 45, 55 and 65⁰C, at optimum conditions of metal concentration of 40ppm for Ni²⁺ and Cu²⁺, 10ppm for Pb²⁺, pH of 10 for Ni²⁺ pH of 8 for Cu²⁺ pH of 4 for Cu²⁺, adsorbent of dose 0.2g Ni²⁺ and Pb²⁺, 1.0g for Cu²⁺, agitation times of 100min Ni²⁺, Pb²⁺, and Cu²⁺ ions. The rate of adsorption was affected by temperature as shown inFigure 10.

The percentage adsorption of nickel(II) decease with increase in temperature from 89.04 to 84.47% at temperature of 25^oC to 65^oC. Percentage adsorption of lead(II) increase from 98.72 to 98.73% at temperature 25^oC to 35^oC and further decrease to 98.24% at 65^oC while percentage adsorption of Copper was observed increase from 91.41 to 93.14% at temperature of 25 to 45^oC and further decrease to 93.01% at temperature 65^oC. These shows that adsorption is endothermic up to the optimum temperature because the extend of adsorption decrease with increase in temperature [ 10].

Analysis of isotherm is very important for designing the adsorption process. The experimental data were analyzed with Langmuir and Freundlich as the two most commonly use isotherms models.

Langmuir adsorption isotherm models the monolayer coverage of the adsorption surfaces and assumes that sorption take place on a structurally homogeneous surface of adsorbent. Freundlich adsorption isotherm models the multilayer adsorption for the sorption on heterogeneous surface [ 10].

Freundlich and Langmuir isotherm model were used to describe the equilibrium data. The Langmuir isotherm constant K₁ and Q_mwere calculated from the slope and intercept of the plot between 1/qe and 1/Ce. The Langmuir isotherm showed good fit to the experimental data with high correlation coefficient in case of Pb²⁺ ions with R² value of 0.9950 over Ni²⁺ and Cu²⁺ ions with R² Value 0.9214 and 0.9908, as is shown in (Table 1). Q_mand K_L were calculated from the slope and intercept respectively.

Freundlich isotherm best fit the experimental data of lead(II) and nickel(II) and with R² value 0.9976 and 0.9937 when compare with that of copper(II) which has R² value 0.9942. Freundlich isotherm constants K_f and 1/n were calculated from the slope and intercept of the straight line of log q_e versus log C_e. The magnitude of n between 1 and 10 (1/n less than 1) represents a favorable adsorption. All information’s are represented in (Table 1). Similar findings reported by [ 11], when determined the adsorption of zinc and copper ions from aqueous solution by thermally treated Quail Eggshell.

Kinetic model were applied to test for the experimental data in order to check the mechanism of the adsorption of the metals ions by Mangiferaindica leaf and the potential rate controlling step mass transport and chemical reactions. Pseudo first-order and Pseudo second-order kinetics model were tested.

The adsorption kinetics described by a Pseudo first-order equation. From the studied initial concentration, the rate constant (K₁) and theoretical equilibrium of adsorption capacities (q_e) was calculated from the slope and intercept of the linearized plot of log(q_e –q_t) against t as shown in the (Table:2). The correlation coefficient (R²) for nickel(II), lead(II) and copper(II) of the linear graph are 0.9058, 0.9059 and 0.6511 as shown in (Table 2). which indicate the data fit well to pseudo first-order model. The calculated value of K₁ and q_e for the nickel(II), lead(II) and copper(II) are 0.031, 0.0598, 0.1681 min^-1 and 1.3313, 30.8810, 21.463 mg g^-1. Therefore it could be suggested that the adsorption of all the metals ions did not fit; pseudo first-order model when compare with the R² value of the pseudo second-order model and the calculated value of q_e.

The experimental data was also applied to the pseudo second-order model given in kinetics model. The fit of this model was controlled by each plot of t/q_t versus t respectively. The constant q_e and k₂ was calculated from the slope and intercept of the shown in (Table 2). It can be seen from the result R² value obtained for Ni²⁺, Pb²⁺ and Cu²⁺ ions are higher than those obtained from pseudo first-order kinetic model, which are 0.9938, 1.00 and 1.00. These suggest that pseudo second-order model best fit adsorption of nickel(II), leadi(II) and copper(II) respectively, the calculated k₂ and q_eare 10.248, 0.00006, 0.00012 min^-1 and 3.093, -1666.7, 416.66mg g^-1. Pseudo second-order model is based on the capacity of phase and indicating that the rate limiting step is chemical adsorption process [ 12].

Thermodynamics parameter of the adsorption process such as change in Gibbs free energy ΔG (KJ/mol), change in enthalpy ΔH (KJ/mol) and change in entropy ΔS 9KJ/molk) , were determined at different temperature. The plot of logk against 1/T gives a linear graph, ΔH and ΔS are determined from the slope and intercept of the graph. The result shows a good R² value 0.9795 for Ni²⁺ but less R² value 0.6734 and 0.6184. Change in Gibbs free energy of the adsorption Ni²⁺, Pb²⁺ and Cu²⁺ ions at different temperature are presented in (Table 3). The negative value of ΔG in case of Ni²⁺, Pb²⁺ ions implies that the process is feasible and spontaneous in nature while the positive value of ΔG for Cu²⁺ ions implies is unfeasible and non-spontaneous [ 9]. The value of change in enthalpy ΔH, and change entropy ΔS, of Ni²⁺, Pb²⁺ and Cu²⁺ ions adsorbed by Mangiferaindica leaf obtained are also present in (Table 3), the positive value of ΔH suggest the endothermic nature of the adsorption and a possible bond which occur between the metals and the adsorbent while the negative suggested exothermic nature [ 13]. The positive value of ΔS indicate increased In degree of randomness at solid solution interface during the adsorption of the metals ions the Mangiferaindica leaf. Similar finding was observed by researchers [ 1].

Removal of Ni²⁺, Pb²⁺ and Cu²⁺ ions from aqueous solution using Mangiferaindica leaf as adsorbent; has been investigated. From the investigation it was observed the experimental parameters at optimum condition of initial metal ion concentration, pH, adsorbent dosage, contact time and temperature was determined for their potential effect on the efficiency of Ni²⁺, Pb²⁺ and Cu²⁺ ions adsorption.

Based on the detailed experimental investigations it was determined to be 40ppm for Ni²⁺ and Cu²⁺ and 10ppm for Pb²⁺ ions, ⁺, 10 for Ni²⁺ 8 for Cu²⁺ 4 for Cu²⁺, 0.2g for Ni²⁺ and Pb²⁺, 1.0g for Cu²⁺, 100min Ni²⁺, Pb²⁺, and Cu²⁺ ions, and 25^oC, 35^oC and 45^oC respectively. The kinetics studies indicate that the adsorption process of the metals ions followed the pseudo second-order model with R² value of 0.9938, 1.00 and 1.00 respectively. Equilibrium studies showed that the adsorption of Ni²⁺, Pb²⁺ and Cu²⁺ ions are well represented by both Langmuir and Freundlich isotherm but the Langmuir model gave a better fit for Pb²⁺ ions with R² value of 0.9950 and Langmuir constant K_L of 4.3383 while Freundlich isotherm model best fit the experimental data of lead(II) and nickel(II) with a R² value of 0.976 and 0.9973 and Freundlich constant K_F value of 4.2677 and 0.0874. The calculated thermodynamics parameters of Ni²⁺, Pb²⁺ and Cu²⁺ ions are; ΔG^o -1182.49, -5479.1 and 613.48 KJ/mol, ΔH^o -8893.84, -5710.25 and 2994.03KJ/mol, and ΔS^o -1.3515, -0.7051 and 7.486KJ/molk. The FT-IR analysis suggested alcohol and alkene groups combine intensively with Ni²⁺, Pb²⁺ and Cu²⁺ ions. The advantage of high metal adsorption, the biomass leaf of Mangiferaindicahas the potential to be used as a simple, efficient, effective methods and economical adsorbent material for the adsorption Ni²⁺, Pb²⁺ and Cu²⁺ ions from waste water.

We Acknowledged Technicla staff of the Department of Chemistry, Biochemistry, pharmacy and Geology of Gombe state University .Gombe State and the University for the Equipment’s and Laboratory space.