INTRODUCTION:

The entire world is focussing on one major issue i.e environmental pollution. It is a serious problem to all kinds of species. The main environmental pollution occurs from process industries and urbanization. The effluents containing trace amounts of metal ion coming from various industries are directly entered into the water bodies. The low concentrated metal ions are not biodegraded easily and causing affects on man and aquatic life¹.

The metals like lead, zinc, cadmium and chromium were the most poisonous heavy metals need to be removed. The heavy metal chromium mainly comes from dyes, toys, pigments and electroplating industries². Even at low concentrations of chromium metal in the effluent causes serious damage to environment³.

The conventional methods available for removal of heavy metals from industrial effluents are filtration, osmosis, electro dialysis and ion exchange, but these are suffering from various problems like sludge formation, high cost, partial removal of metal ions^4-5.

So, there was a need of process, which is low cost, no sludge formation and zero pollution, to meet all these biosorption, is a suitable method for removing toxic metal ions from waste water^6-7.

The biosorbent Tamarind fruit shell (Tamarindus indica) was derived from tamarind tree as a waste material. Tamarind trees were grown in any dry area. The hard shells were removed from the fruit before using in food. The shells are discarded as waste material⁸. So, this was a low cost and easily available biomass used for the removal of metals from the wastewater. Many researchers were done the work on this for the removal of chromium⁹.

The main objective of this investigation is to find the ability of tamarind fruit shell biosorbent for biosorption of chromium by estimating the various process conditions of agitation time, dosage, metal ion concentration, pH, equilibrium isotherms and kinetic parameters.

MATERIAL AND METHODS:

Biosorbent preparation:

The tamarind fruit shells were taken from tamarind trees in Guntur district of A. P. The tamarind fruit shells were cleaned with double distilled water. The cleaned shells were dried at a temperature of 45^OC in a drier. The dried shells were grounded by using ball mill and then sieved for separating the various size particles. The required size particles were stores in air tight bottles for further use as a biosorbent¹⁰.

Standard solution:

The chromium metal standard solution was prepared with 1.5gm of potassium dichromate dissolving in 1litre of deionized water. The desired concentrations of stock solutions were prepared by appropriate dilution. The pH of the solution was adjusted with 1N hydrochloric acid.

Experimental work:

The percentage removal of chromium using tamarind fruit shell powder was estimated with batch biosorption experiment. The process conditions such as agitation time, dosage, ion concentration and pH were estimated. The biosorption experiment was conducted by taking 1.2gm of biosorbent in a conical flask consisting of 25 ml stock solution. The sample was maintined the process conditions of dosage 1.2gm,pH 5,metal ion concentration of 5 mg/l/ find the optimum contact time.The flask was kept in an agitator for 1 hour with a speed of 180 RPM at room temperature. After agitation the sample was filtered and then determines the final concentration using spectrophotometer. The % removal of chromium was calculated by

% Removal of chromium = (C_i-C_c) / C_i * 100

Here C_i(mg/l) initial concentration of the sample, C_c(mg/l) final concentration of the sample. The similar procedure will be followed to find the other process conditions and to find the kinetic, isotherm and thermodynamic parameters.

RESULTS AND DISCUSSION:

Figure.1 Percentage removal of chromium with agitation time

In biosorption of chromium onto the tamarind fruit shell powder the data showed agitation time of 50 min was required to get optimum as shown in figure.1. The sorption did not change effectively with further increase in agitation time¹¹. The chromium removal increased with increase in time because of more surface area available for metal sorption on the biosorbent. This value was taken in further experiments as a basis to get other parameters¹².

Effect of dosage:

Figure.2 Percentage removal of chromium with dosage

The influence of biomass dose on metal removal was determined by taking dosage range of 0.1-1.2 g and results were presented in figure.2.As dosage increases from 0.1 to 1.2 gm, the chromium percentage removal was raised from 55% to 82%.The increase in metal removal was because of high number of binding sites available for sorption of sorbate as dosage increased from 0.1 to 1.2gm this was shown in figure.2, after this it reached to saturation¹³.

Influence of metal concentration:

Figure.3 Metal ion concentration with change in chromium removal

The variation of metal concentration on removal of chromium with tamarind fruit shell powder was shown in figure.3.The concentration from 5-80mg/l was considered for evaluating the change of metal removal. From figure it was cleared that at metal concentration of 5 mg/l was given more biosorption than other concentrations¹⁴. The % biosorption of metal ion was decreased with increase in concentration because more binding sites were present at low concentration than at higher concentration level, at higher concentration the sites were saturated hence less removal was appeared¹⁶.

Effect of pH:

Figure.4 Percentage removal of chromium with pH

The influence of pH on removal of chromium was presented in figure.4. From figure as pH increased from 1-5, the chromium percentage removal was also increased from 70-81%.After this the percentage removal was decreased from 81-50% from pH 6-11.At low pH values high rate of metal removal was noticed because of more number of H+ ions bind with the functional groups on the surface of the biosorbent. After pH 5, the decrease in percentage removal was due to precipitation of metal ion^17-18.

Isotherms:

The isotherms of arsenate biosorption using tamarind fruit shell powder were presented in figure.5 and figure.6, respectively. From below plots, the given data were tested to the following isotherms by nonlinear regression analysis¹⁹.

Freundlich: q_e= k_fc_e^1/n

Here, q_e – amount of solute/solvent (mg/g), c_e - concentration at equilibrium (mg/L), k_f,,n - equilibrium constants. The results were obtained with linear plot of log c_e Vs log q_e.

Langmuir: q_e = k_L c_e / (1+a_Lc_e)

Here, q_e - amount of solute / adsorbent (mg/g), C_e -concentration at equilibrium (mg/L), a_L is the constant and k_L is the Langmuir constant. The data obtained with linear plot of c_e Vs c_e/q_e.

The results revealed that the given data were well followed to Langmuir isotherm than Freundlich isotherm^20-21.

Figure.5 Freundlich isotherm

Figure.6 Langmuir isotherm

Kinetic study:

The biosorbent efficiency was estimated using kinetic models namely first and second order kinetics. The adsorption mechanism and characteristics were also determined with kinetic study.

First order expression: Log ( q_e-q_t) = log q_e - (k₁/2.303) t

Here, q_e and q_t are biosorption capacities at time t and at equilibrium conditions. The values of slope and intercept were estimated from the plot of Log (q_e-q_t) Vs t as shown in figure.7. The plot it was stated that the data were not followed the first order kinetics. The value of regression coefficient R² is not much closer to one. So, the second order model was tested^21-22.

Second order expression: t/ q_t = 1/k₂ q_e² + (1/q_e) t

Here, q_e and q_t- biosorprtion capacities, k_2-rate constant. The regression coefficient R² is 0.993 and is very close to one shown in figure.8. Hence the given data well correlated to second order kinetics^23-24.

Figure.7 First order kinetics

Second order:

Figure. 8 Second order kinetics

Thermodynamics:

In order to determine the thermodynamic behaviour on biosorption of chromium onto the tamarind fruit shell. The thermodynamic parameters were evaluated using the following equations:

ΔG^o= -RT lnK

lnK= ΔS^o/ R –/ RT

Here, ΔG^o Gibbs free energy, ΔS^oentropy, ΔH^o enthalpy and K-dilution coefficient²⁵.

Table. 1 Thermodynamics

S.No	Initial Conc., C₀, mg/l	*∆H,* J/mol	∆S J/mol-K	*∆G at different temperatures* J/mol
S.No	Initial Conc., C₀, mg/l	*∆H,* J/mol	∆S J/mol-K	293 K	303 K	313 K	323 K	333 K
1	20	23.57	53.745	-15723.7	-16261.2	-16798.6	-17336	-17874
2	40	24.77	54.645	-15986.2	-16532.7	-17079.1	-17626	-18172
3	60	18.113	29.409	-8598.72	-8892.81	-9186.9	-9481	-9775.1
4	80	22.21	42.64	-12471.3	-12897.7	-13324.1	-13751	-14177
5	100	16.84	22.727	-6642.17	-6869.44	-7096.71	-7324	-7551.3

From Table.1, the negative values of Gibbs free energy were indicated the spontaneous nature of the biosorption process. The positive values of enthalpy were stated that the given process was endothermic^26-27.

CONCLUSIONS:

The potential of tamarind fruit shell powder to remove chromium from wastewater was investigated. A biosorption process onto a Tamarindus indica a low cost, easily available biosorbent, is a technique applied for biosorption of chromium. The optimum process conditions were found to be agitation time 50 minutes, dosage 1.2gm,initial metal ion concentration 5mg/l and pH 5.The experimental data best correlated to Langmuir isotherm than Freundlich isotherm. The kinetic data followed the second order kinetics. The thermodynamic parameters revealed that the biosorption process was spontaneous and endothermic. The maximum percentage removal of chromium is 82%.The experimental results suggested that the tamarind fruit shell powder is a favourable biosorbent for removal of chromium from waste water.

CONFLICT OF INTEREST:

No conflict of interest.

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Received on 09.09.2019 Modified on 12.10.2019

Research J. Pharm. and Tech 2020; 13(5): 2340-2344.

DOI: 10.5958/0974-360X.2020.00421.7