REV.CHIM.(Bucharest)♦68♦No. 3 ♦2017 http://www.revistadechimie.ro 527 The heavy metals are undestroyable elements, the most of them having toxic effects on living organisms when exceeding a certain concentration. Some heavy metals (like cadmium and zinc) may pose a risk to human health when transferred to the food chain. The sources of heavy metals in soil are different. In the case of cadmium and zinc ions, soil contamination occurs by the addition of phosphate fertilizers, sewage sludge and especially metallurgical activities. [1-5] Once in soil some of the metals would be persistent because of their immobile nature. Other metals however would be more mobile. This mobility must be taken into account when the food chain is concerned. Pollution problem arise when heavy metals are mobilized into the soil solution and taken by plants. The main factors influencing the adsorption of heavy metals in soils are the following: the p H, the soil organic matter (SOM) content, the ionic strength, the cation and anion index, the soil texture, the pore structure, the residual time and the temperature. In general, sorption increases with increasing p H. The lower the p H value the more metal can be found in solution as a result of the increased proton concentration. The Cd 2+ and Zn 2+ ions are found in exchangeable form, suggesting that these metals are relatively very mobile. The soil organic matter (SOM) is very important for the retention of metals by soil solids, because of the humic acid (HA) presence; the complexation of HA at higher pH is responsible for dissolution of some metals from soil [6]. Naidu and Harter [7] reported that the role of organic acids in Cd 2+ mobilization is especially important. Complexation of metals by organic ligands play an important role in controlling metal solubility. Metal-ligand complex stability generally decreases with pH reduction, reflecting the role of RCOO - in metal complexation. The ligands include low molecular weight organic acids like citric, oxalic, formic, acetic, succinic, malonic. Highest amount of Cd 2+ was released by acetat and malate ones. The Adsorption of Cadmium and Zinc Ions from Waste Waters in Agricultural Argilaceous Soils IRINA PINCOVSCHI 1 , NICOLETA NEACSU 2 , CRISTINA MODROGAN 3 *, MIRCEA STEFAN 2 1 University Politehnica of Bucharest, Department of Hydraulics, Hydraulic Machinery and Environmental Engineering, 1-7 Polizu Str., 011061, Bucharest, Romania 2 University Politehnica of Bucharest, Faculty of Applied Chemistry and Materials Science, 1-7 Polizu Str., 011061, Bucharest, Romania 3 University Politehnica of Bucharest, Faculty of Applied Chemistry and Materials Science, 1-7 Polizu Str., 011061, Bucharest, Romania The adsorption of cadmium and zinc ions from waste waters in agricultural argilaceaus soils have been studied, using a thermodynamic method in order to put in evidence the influence of adsorption conditions on adsorption degree. The adsorption isotherms, Langmuir and Freundlich, have been used to describe the adsorption equilibrium. The experimental data put in evidence that Cd 2+ ions are more adsorbable (about 300 μmol/g) than Zn 2+ ones (about 200 μmol/g). The Langmuir isotherms reflect more exactly the adsorption process of both Cd 2+ and Zn 2+ ions, being recommended for thermodynamic parameters determination. Keywords: industrial waste waters, Cd 2+ and Zn 2+ adsorption, agricultural argillaceous soils * email: c_modrogan@yahoo.com To separate the p H effect from ligand ion effect it was found that at high p H values Cd 2+ - ligand ion complexation was essential for the solubilisation of Cd 2+ . The amount of metals adsorbed decreases with increasing ionic strength [8]. It was underlined that, there was an increase of Zn 2+ adsorption with p H elevation and a reduction of ionic strength of background electrolyte. Results showed that the metal ion was more strongly adsorbed at lower ionic strengths, while any increases in electrolyte concentration produce a decrease in metal adsorption. Thus, soils with higher ionic strength may have more risk of metal leaching from sevage sludge disposal than soil with lower ionic strength [9, 10]. The soil texture plays an important role in mobility of metal in soil. Texture reflects the particle size distribution of the soil and thus the content of fine particles like oxide and clay. The clay soil retains high amount of metal when compared to sandy soil. The cation and anion index has a big importance in metal adsorption in soil. The anions can contribute in reducing heavy metal adsorption by the possible formation of negatively charged or neutral species like: MCl 2 , MCl 3 - , MCl 4 - . Cd 2+ is known to form relatively stable Cl - complexes, which greatly influence the mobility of metals in soils. The ability of Cl - to maintain relatively high concentration of heavy metals in soil solution may produce favorable conditions for faster leaching of metals. The mobility of Cd 2+ in soil increases at higher Cl - concentration. The effect of Cl - on Cd 2+ uptake could be explained by the presence of CdCl n 2-n species. The presence of hydrous iron oxides and hydrous manganese oxides has an immobilizing affect of Cd 2+ in soil [11, 12].Competing ions can have a marked effect on ion sorption by soils [13-15] the presence of Pb 2+ can determine a decreasing of Cd 2+ adsorption [17, 18]. Also, the effect of Cd 2+ on plant metabolism could be reversed by Mn 2+ presence in soil [19, 20].