Influence of pH value on Cu (II) biosorption by lignocellulose peach shell waste material

Abstract

In the last decade, the pollution made by anthropogenic sources has reached large amounts with special attention on heavy metals because of their high toxicity, persistence and bioaccumulation tendency. Since the conventional methods for their removing are either too expensive or create large quantities of toxic sludge, the great attention has been paid to the new technologies such as biosorption, technology that use cheap, abundant, organic waste for sequestering pollutants from contaminated mediums. Among the other factors that affect biosorption process, pH value is one the most important because it directs both the metal solution chemistry as well as the activity of the biomass functional groups. In this paper the influence of pH value on biosorption of Cu (II) by unmodified low-cost lignocellulose biosorbent - peach shell (PS) particles, have been studied. The chemical composition of PS, point of zero charge (pHPZC) as well as its surface morphology is also presented. Results have showed that this biosorbent contains mainly cellulose and lignin, the components that carry the functional groups responsible for metal binding. Its multilayer surface contains many pores and channels that help diffusion in deeper layers and force biosorption process. Point of zero charge determination was performed with three different KNO3 ionic strengths: 0,1M, 0,01M and 0,001M. The obtained value for pHPZC was 4,75±0,1 and showed that this biosorbent is non-sensitive to ionic strength of electrolyte applied. Biosorption experiments were done with peach shell particles whose diameter was -0,5+0,1mm at 25oC . The initial copper (II) concentration was 50 mg/dm3 while the biosorbent concentration was 10g/dm3. Experiments were done with and without keeping pH constant. The influence of pH on biosorption process was examined in 2-6 pH range. The percentage of Cu (II) removed by PS, reaches its maximum at pH 6, with the 90,43% removing but this percentage can also be attributed to precipitating of metal at this pH value. However, under the same operational conditions, but at pH 2, the retention of copper is equal to 2,62%. The results also indicate that it is necessary to lead the biosorption process with keeping pH constant all the time, since the copper removal was about 46 % less when the pH value was not kept constant during the biosorption process. The pH value obtained as optimal was slightly higher than pHPZC value which indicates that electrostatic attraction is one of the possible binding mechanisms in biosorption process. The results have showed that the removal of Cu (II) with peach shell particles is very sensitive to solution pH and that this parameter should be thoroughly investigated and strongly controlled during the whole removal process.

Keywords

• biosorption
• copper ions
• peach stone
• zero point charge
• pH value