The wide use of heavy metals and its compounds by modern industries has resulted in large quantities of this element being discharged into environment. These inorganic micro-pollutants are of considerable concern because they are non-biodegradable, highly toxic and have a probable carcinogenic effect. If directly discharged into the sewage system, their presence decreases the efficiency of the biological treatment [1, 2, 3].
Among the heavy metals, chromium is one of the most important environmental issues. Most of the chromium is discharged into aqueous waste as a Cr(VI) and Cr(III). A wide range of technologies are available for the removal of Cr(IV) and Cr(III) from ...view middle of the document...
Guava leaf is a waste and has pores that can function as a bio-sorbent. Cr (VI) used in this study is a solution of K2Cr2O7.
Experiment. The experiment was carried out by batch process. The Cr(VI) solutions were treated in an experimental system consisting of a flask shaker, a 300 mL erlenmayer. The K2Cr2O7 in concentration of 1 ppm (0,03 gram) was mixed with 1000 mL of water in the erlenmayer. A total of 200 mL sample with a concentration of 1 ppm K2Cr2O7 incorporated into 250-ml Erlenmeyer flask which already contains the bio-sorbent. Bio-sorbent dosage varied as much as 1 gram, 2 grams, 3 grams, 4 grams, and 5 grams. The content of the erlenmayer was shaken at 350 rpm for varied contact times (5 minutes, 10 minutes, 20 minutes, 30 minutes, 60 minutes, 90 minutes, 120 minutes and 150 minutes) and then settled for 30 min. The precipitate was separated from the solutions by filtration through Whatman 41 filter paper. The filtrates were analysed for residual Cr(VI) using atomic absorption spectrophotometer (AAS). The experimental conditions are shown in Table 1.
Table 1. Experimental conditions
Initial Cr6+ concentration [ppm]
Bio-sorbent dosage (gram)
Contact time [min]
Precipitation time [min]
1 – 5
50 – 150
Mathematical models. Mathematical model used is the Langmuir adsorption isotherm, Freundlich isotherm and adsorption kinetics. Assumptions used in the Langmuir models are: (1) the surface of the adsorbent has the same activity (homogeneous), (2) there is no interaction of the adsorbed molecules, (3) adsorption mechanisms that occur together, and (4) adsorption occurs only on one layer equation. Based on these assumptions, the Langmuir equation  can be written as:
Where is maximum amount of heavy metal ions unity adsorbent (mg sorbate/g adsorbent), b is the binding affinity (L/mg sorbate) and ce is the concentration (mg adsorbate/L). Equilibrium curve obtained by plotting the 1/ce and 1/qe, in order to obtain the slope and intercept. Value of K is equal to 1/b. While the Freundlich isotherm models are based on the assumption that the adsorbent has a heterogeneous surface and each molecule has the potential absorption of different, so the Freundlich equation  stated:
Where KF and ce are constants and are obtained from the experiment. A value of 1/n is the slope of plot log qe with log ce. The KF value depends on the value of n. To determine the kinetics of sorption rate of Cr(VI) removal using guava leaves (Psidium guajava), this study uses Lagergren's rate equation. Rate equation consists of a quasi-order kinetics model (Equation 3) and the pseudo second order kinetics model (Equation 4).
Results and Discussion
The Cr(VI) removal was studied under different conditions, viz. pH (4-8) and contact time (50–150 min).
Effect of pH on...