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Neste artigo, o potencial no qual a depressão da ga lena ocorre, é relacionado com a formação de compostos hidrofílicos em sua superfície. São propostas reações com base em voltametria cíclica, da dos termodinâmicos e análises por espectroscopia de fotoelétrons. Variáveis eletroquímicas, tais como o potencial de oxirredução, apresentam boas perspectivas para a flotação seletiva da ga lena e esfalerita, pois numa dada faixa de potencial, a superfície da ga lena, ao contrário da esfalerita, se torna hidrofílica, conforme mostraram as medidas de ângulo de contato e tes tes de microflotação.In this ar ti cle, the po ten tial at which ga lena de pres sion oc curs is re lated to the for ma tion of hy dro philic com pounds on its sur face. Re ac tions are pro posed based on anal y ses by cy clic voltammetry, ther mo dy namic data, and X-ray pho to elec tron spec tros copy (XPS). Elec trochem i cal vari ables, such as the re dox po ten tial, pres ent good per spec tives for se lec tiv ity in the flo ta tion of ga lena and sphalerite, be cause in a given range of po ten tials, the ga lena sur face becomes hy dro philic, as shown by mea sure ments of the con tact an gle and floatability tests. Key words: ga lena elec tro chem is try, con tact an gle, de pres sion, sphalerite In tro duc tionThe flo ta tion of sul fide min er als, us ing ore with complex com po si tion, has been ex ten sively stud ied, as shown by lit er a ture re views; the pur pose is to ob tain se lec tiv ity in the pro cess [1][2][3][4] . Some de pres sants and ac ti va tors are al ready well known, such as cy a nide and zinc sul fate. In cases of mix tures of lead, cop per, and zinc min er als , the se lec tiv ity is poor, and the lead con cen trates be come highly con tam inated by the other min er als which orig i nate from the lead ore.The main lead ore is lead sul fide, ga lena, with a the o reti cal con tent of 86 wt% Pb. It oc curs nat u rally, ac com pa nied by other sul fides and gangue min er als. The clas sic pro cess of ore dress ing ap plies thiocollectors, such as xan thates, in a pH range of 8 to 9; the re sult ing con cen trate is 60% Pb 5,6 . How ever, the mech a nism of the re ac tion has not yet been solved 7,8 . The old est the ory 9 ex plains the pro cess as one of ad sorp tion, with ion ex change be tween the an ions xanthate and sul fide oc cur ring on the sur face of the min eral. It is widely rec og nized that ox y gen is es sen tial to the flo ta tion pro cess 10-14 .In the first step of the chem i cal mech a nism, the ga lena sur face sul fide ion is ox i dized, pro duc ing lead sul fate and thiosulfate, and the lat ter re acts with xanthate ion X -, as follows The hy dro pho bic char ac ter of the ga lena sur face is attrib uted to PbX2.In the elec tro chem i cal mech a nism, elec trode re ac tions oc cur on the ga lena sur face which is in con tact with the aque ous so lu tion con tain ing xanthate ion, as fol lows 15 : Ar ti cle

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Fulvic (FA) and humic acids (HA) from the solubilization of organic matter are significant agents of the complex of metallic ions in soil and water. Cadmium ions are important natural water pollutants which are discharged along with electroplating and zinc metallurgy liquid wastes, zinc and cadmium being always associated with isomorphic substitution. In this paper we study the complexes formed by Zn 2+ and Cd 2+ with fulvic acids, using computational chemistry. We carried out relative free energy calculations using a thermodynamic cycle and Free Energy Pertubation (FEP) and Density Functional Theory (DFT-B3LYP/6-31G**) methods. We also computed the interaction energies between orbitals from Natural Bond Order (NBO) calculations. Cd-FA complexes, octahedral with four water molecules in the coordination sphere are more stable than Zn-FA complexes, tetrahedral with two water molecules. This means that FA should be a better ligand for Cd 2+ bioavailability and toxicity in natural aquatic environments.