REMOVAL OF CUPRIC IONS IN AQUEOUS SOLUTION BY ADSORPTION ON BARKS OF DACRYODES EDULIS AND MANGIFERA INDICA

Martin Tchoumou 1 , Kimbassa Mahoungou Fréderic Guenol 1 and Mouelet Cédric 2 . 1. Faculty of Sciences and Technology, University Marien NGOUABI, Brazzaville, CONGO. 2. Normal Superior School, University Marien NGOUABI, Brazzaville, CONGO. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

The adsorption of the cupric ions on bark of dacryodes edulis and mangifera indica was studied under various experimental conditions with an aqueous solution of concentration 63,55 mg/L. The effect of adsorbent dosage, the contact time and the pH of solution was examined. In all cases, the percentage of adsorbed metal increases with the contact time and the adsorbent dosage; it takes two hours of contact time to reach equilibrium with the bark of mangifera indica, whereas one needs of them three hours for those of dacryodes edulis. On the other hand, the effect of pH on the percentage of adsorbed metal is not the same in both cases since the maximum adsorption on the bark of mangifera indica is located between pH 5 and 6, whereas with the bark of dacryodes edulis, the pH is higher than 6. The results obtained showed that the bark of mangifera indica adsorbed the quantities of copper larger than those of dacryodes edulis; the maximum adsorption capacity determined by the interpretation of the model of Langmuir isotherms are 5,85 mg/g for the bark of mangifera indica, and 5,22 mg/g for those of dacryodes eludis.

Introduction:-
Industrial development caused these last years the increase in the quantities of the liquid effluents charged in heavy metals in many countries which it is necessary to reject into the receiving medium. If these effluents are not treated before their rejection, they can generate the disappearance of certain plants and animals species (

Materials and methods:-
The barks of mangifera indica and dacryodes edulis were collected from trees in a district of Brazzaville in Republic of CONGO. These barks were washed with the tap water and dried in sunlight during three weeks, then dried in an oven with 105° C during three hours before being crushed and filtered until a granulometry of 75μm.
Before their use as adsorbent, they were washed with the distilled water at a quantity of 50 g in 2 liters under agitation during three hours in order to eliminate the residues of crushing and the organic compounds likely to color the solution and to disturb the determination of cupric ions using spectrophotometric method (Bandela et al.,2016).
The stock solution containing the cupric ions was prepared by dissolving a given quantity of Cu(NO 3 ) 2 , 6H 2 O in distilled water and the desired solution with the concentration of 63.55 mg/L was obtained by dilution.
The contact of the adsorbent with the solution of cupric ions was carried out in beakers of 100 ml containing 50 ml of cupric ions under agitation and various experimental conditions; After separation of the mixture adsorbent / solution by filtration, the cupric ions were analyzed with a spectrophotometer Aqualytic AL 800, with the wavelength of 800 nm by using the method of the calibration curve (Nassima and Moussa, 2010).
. The equilibrium adsorption capacity qe(mg/g) was determined by the following relation . The separation factor R L = .
. was used to know if adsorption is favorable or unfavorable (Ackacha and Meftah, 2014).  This curve shows that in each case, the speed is fast at the beginning and decrease with time. It takes two hours of contact time to reach the equilibrium of adsorption with the barks of mangifera indica whereas one needs of them three hours with the barks of dacryodes edulis. When equilibrium is reached, the percentage of the adsorbed metal on the barks of mangifera indica is higher than that obtained on the barks of dacryodes edulis. This difference can be explained amongst other things by the chemical composition and properties which are not the same for the two adsorbents, in particular the number of adsorption sites and specific surface.

Influence of the pH on the percentage of adsorption:-
The effect of the pH was studied in the interval from 2 to 6 for a contact time of two hours ; the maximum value of the pH equal to 6 was retained to avoid the precipitation of the cupric ions which would be likely to cause an interaction between the phenomena of adsorption and precipitation of Cu(OH) 2 (Ackacha and Meftah, 2014).
The figure 3 shows the variations of the percentage of the adsorbed metal as function of the pH of the solution for each adsorbent. to those which we obtained on mangifera indica and these authors explain the variation by interactions between the species Cu 2+ , Cu(OH) + and the functional groups present at the surface of the adsorbent.
In addition, Ksakas et al., (2015) studied the adsorption of the ions Cr (VI) on vegetable materials and allocated this variation by the existence of the electrostatic forces between the surface of the adsorbent and the various species charged with chromium present in the solution according to the pH.
Indeed, according to the pH of the solution, the particles of the adsorbent can be charged negatively or positively so as to have effects on the electrostatic attraction forces between the ion and the adsorbent (Kumar et al.,2014).
On the other hand, this percentage does not pass by a maximum with the barks of dacroydes edulis . We think that this difference in behavior of the Cu 2+ ions on the two adsorbents can be explained by the fact that they do not have the same surface properties.

Determination of the maximum adsorption capacity:-
The determination of the maximum adsorption capacity was carried out by exploiting the linear relation of the Langmuir isotherm. Figure 4 represents the variations of 1/qe as function of 1/Ce obtained during the adsorption of the cupric ions on the barks of mangifera indica In the same way, the maximum adsorption capacity on dacroydes edulis is q max = 5. 22

Conclusion:-
The objective of this work was to study the possibility of eliminating the cupric ions in aqueous solution by adsorption on barks of mangifera indica and dacryodes edulis. The results obtained showed that these two adsorbents can be used to adsorb cupric ions in aqueous solution, although the eliminated quantities are not too large when one them compared to other adsorbents. The percentage of adsorbed metal is function oh pH; contact time and adsorbent dosage.
. In both cases, the contact time between the solution and the adsorbent to reach equilibrium is two to three hours according to the adsorbent whereas the best percentage of adsorption is obtained between pH 5 and 6. The percentage of absorbed metal is higher on the barks of mangifera indica compared to those of dacryodes edulis . The determination of the maximum adsorption capacities by the exploitation of the Langmuir isotherms gave 5.85 and 5.22 mg/g respectively on the barks of mangifera indica and dacryodes edulis . The value of the separation factor higher than zero in both cases indicated that the adsorption of the cupric ions is favorable on these two adsorbents.