RESUMO
In the present work, the usefulness of grape stalks wastes generated in the wine production process has been investigated for the removal of copper and nickel ions from aqueous solutions. The sorption process was relatively fast and equilibrium was reached after about 60 min of contact. The influence of pH, sodium chloride and metal concentration on metal removal has been studied. Uptake showed a pH-dependent profile. Maximum sorption for both metals was found to occur at around pH 5.5-6.0. An increase of sodium chloride concentration caused a decrease in metal removal. Langmuir isotherms, at pH 6.0, for each metal were used to describe sorption equilibrium data. Maximum uptake obtained was 1.59x10(-4) mol of copper and 1.81x10(-4) mol of nickel per gram of dry sorbent. Sorption of copper and nickel on grape stalks released an equivalent amount of alkaline and alkaline earth metals (K+, Mg2+, Ca2+) and protons, indicating that ionic exchange is predominantly responsible for metal ion uptake. Fourier transform infrared (FTIR) spectrometry analysis indicated that lignin C-O bond might be involved in metal uptake. Equilibrium batch sorption studies were also performed using a two metal system containing (Cu(II)+Ni(II)). In the evaluation of the two metal sorption system performance, single isotherm curves had to be replaced by three-dimensional sorption isotherm surface. In order to describe the isotherm surface mathematically, the extended-Langmuir model was used. Nickel was found to be much more sensitive to the presence of copper than copper is to the presence of nickel.
