Uticaj pH vrednosti na biosorpciju jona bakra otpadnom lignoceluloznom masom koštice breskve

Abstract

Jedan od glavnih faktora u procesu biosorpcije predstavlja pH vrednost rastvora sorbata, jer istovremeno utiče na hemijsko ponašanje prisutnih kontaminanata kao i na aktivnost funkcionalnih grupa biosorbenta. U ovom radu ispitan je uticaj pH vrednosti u procesu biosorpcije dvovalentnog bakra, nemodifikovanom otpadnom lignoceluloznom masom koštica breskve (KB). Procenat uklanjanja bakra ovim biosorbentom znatno varira u ispitivanom opsegu pH vrednosti, počev od 2,62% za pH vrednost 2, do 90,43% za pH vrednost 6, pri inicijalnoj koncentraciji bakra od 50 mg/l. Rezultati ispitivanja pokazali su da je za KB pri izabranim operativnim uslovima, proces neophodno voditi na pH 5, što je vrednost nešto viša od vrednosti nultog naelektrisanja (pHpzc) koja iznosi 4,75±0,1. Potvrđena je neophod-nost održavanja pH vrednosti konstantnom za vreme procesa, pri čemu je biosorpcioni kapacitet KB dvostruko veći od biosorpcionog kapaciteta bez održavanja pH vrednosti.

In the last decade, pollution from anthropogenic sources has reached high levels. Special attention is being paid to heavy metals because of their high toxicity, persistence and bioaccumulation tendency. Since the conventional methods for their removal are either too expensive or create large quantities of toxic sludge, attention has been turning to 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 of 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, has been studied. The chemical composition of PS, point of zero charge (pHPZC), as well as its surface morphology is also presented. The results 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: 0.1, 0.01 and 0.001 M. The obtained value for pHPZC was 4.75±0.1 and showed that this biosorbent is non-sensitive to the ionic strength of the electrolyte applied. Biosorption experiments were done with peach shell particles of diameters 0.5+0.1 mm at 25°C. The initial copper (II) concentration was 50 mg/dm3 while the biosorbent concentration was 10 g/dm3. Experiments were performed with and without keeping the pH constant. The influence of pH on biosorption process was examined in a pH range of 2-6. The percentage of Cu (II) removed by PS reached its maximum at pH 6, with 90.43% removal, but this percentage can also be attributed to the precipitation of metal at this pH value. However, under the same operational conditions, but at pH 2, the retention of copper was equal to 2.62%. The results also indicate that it is necessary to lead the biosorption process with keeping the pH constant at all times, 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 the 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.