Investigative Study on the Detoxification of Chromium III Ion (Cr3+) Polluted Water Using Neem Leaves as Adsorbent

Abstract

This research work is being carried out in order to ascertain the presence and level of dissolved chromium III ion (Cr³⁺) in water, vegetables and soil of farm land and to investigate the production of an adsorbent from natural source and its use for the removal of the metal ion (Cr³⁺) from the affected water. The presence and level of dissolved chromium III ion (Cr³⁺) in the water, vegetable and the soil samples were ascertained using simple qualitative test and AAS (Atomic leaves) respectively.

Powdered Azadiracta indica leaves (Neem leaves) were prepared and used as adsorbent as against the use of activated carbon, silica, alumina etc.

The equilibrium study was systematically carried out in a batch process covering process parameters such as agitation time, adsorbent dosage and pH of the chromium solution. The effect of the variation of equilibrium agitation time was considered by plotting % removal of Cr³⁺ against agitation time and found out that as time increases, the rate at which chromium ion is being adsorbed by the adsorbent increases, indicating a removal efficiency of 89.2% at 5min. for the water and a maximum of 92.5% at equilibrium time of 60min probably due to weak interaction between Cr³⁺ and the adsorbent with constant stirring. The result of varying the adsorbent dosage to give the idea of the percentage removal of Cr³⁺ in 60min agitation time indicated an increase in adsorption from 89.2% to 89.4% as the amount of neem powder increases from 2g to 10g. This is probably due to an increase in surface area of attachment of the Cr³⁺ to the adsorbent whose surface area has been increased due to the large quantity of it being used. The results of the effect of variation of concentration indicate a decrease in % removal of Cr³⁺ from 95.3% to 62.2% as the initial concentration of Cr³⁺ increases from 10mg/L to 50mg/L for 10g of 106µm, size adsorbent at 60min equilibrium agitation time. The results of the effect of pH variation shows that the % removal of Cr³⁺ from the water increases from 89.2% to 96.8% with 6g of 106µm adsorbent for an increase in pH from 2 to 6. Thus adsorption increases with decrease in acidity, since at low pH, H+ competes with Cr³⁺ for sites on the adsorbent.

Based on the above results which show the maximum % removal of Cr³⁺ higher adsorption of Cr³⁺ heavy metal ion on the adsorbent, there is the possibility of electrostatic interaction or attraction between the adsorbent and Cr³⁺ adsorbent. The possibility of the neem leaves powder containing higher % electronegative components and polar groups like –NH₂ –COOH, OH etc., providing negative surface and making the attraction possible is also thought in this study.

From the results of the AAS and the qualitative test on the soil and vegetable samples, the presence of (Cr^3t) was confirmed though at a low level of 0.000352 ppm and 0.000537 ppm respectively for each of the samples.