Nanoparticle-based sensors for detection of thiourea in hydrometallurgical operations

AGUSTÍN TASHDJIAN, IGNACIO PEDRE, FERNANDO BATTAGLINI, GLADIS J. LABRADA DELGADO, M. GUADALUPE SÁNCHEZ-LOREDO, GRACIELA A. GONZÁLEZ

Leipzig

Conferencia; 15rh EucheMs lnterntiona conference on Chemistry and the Environment; 2015

European Chemical Sciences

The use of species such as thiourea, thiosulphate orcyanide ions is strongly linked to the electroplating, electrowinning, andelectrorefining of metals, as well as to mining activities. Given the environmentalimportance of these pollutants is relevant to achieve a more rational useconsolidating a competitive industry with the introduction of effectiveenvironmental management. The development of suitable sensors for use inproduction processes, as well as those aimed at monitoring effluents,contributes to better use and re-use of hazardous reagents. In this work, novel and easy-to-use colorimetric andelectrochemical thiourea (TU) screen-printed sensors based on immobilizedpolyvinylpyrrolidone-stabilized silver nanoparticles (PVP-AgNPs) are presented.These sensorsare aimed for its direct application in a) leaching solutions of wasteof electrical and electronic equipment, containingsignificant thiourea andcopper amounts, and b) copper electrorefinery baths, where thiourea is added asan additive in small amounts.  Quantitative analysis was carried out by addingdifferent thiourea amounts into synthetic solutions simulating the electrolyticbath,and the leaching solutions. For the colorimetric sensor the absorptionchanges of the surface plasmon resonance band (SPRB) were monitored by UV?Visspectrophotometry. A linear correlation between the absorbance change andthiourea concentration was obtained, ranging from 0.125 ppm to 1 ppm. Ourtechnique has the advantage of working in acidic and high ionic concentratedsolutions.  For the electrochemical sensor, changes in theoverallsurface charge of AgNPs resulting in changes in the charge-transfer resistancefor the copper ions were evaluatedby electrochemical impedance spectroscopy.Thecharge-transfer resistance, calculated from Randlesmodified equivalent circuitfrom the spectra,was plotted versus thiourea concentration,showing excellentlinear correlation (R2 =0.932 and detectionlimit 0.133 gL-1), and verygood reproducibility,employing different modified electrodes for eachexperiment (standard deviation for 3 independent experimentswere: 9% for 0thiourea measurements, less than 5% for0.250?0.750 gL-1 and 13% for1 gL-1).Affinity between AgNPs or thiourea and cations suchas Cu2+or Fe3+ could affect the performance of thissensor(Akeneev et al. 2005, Ratnarathornet al.2012), and for this reason the charge transfer resistantvalues asfunction of thiourea concentration were evaluated ina bath containing Cu(II),Fe(III) and trace amounts ofgold and silver were fitted for 0, 0.250, 0.500,0.750 and1 gL-1showing a linear correlation, too, with anaveragesensitivity of (34±3) W/(gL-1),R2=0.975 and limit of detectionof 0.143 gL-1. The effect of different experimental conditions duringthe nanoparticle synthesis was analyzed and the system of immobilized PVP-AgNPswas characterized by Field Emission Scanning Electron Microscopy (FESEM). Theproposed systems provide simple, economical, easy-to-handle and rapid measurementtools for monitoring hydrometallurgical processes for optimizing thereconditioning of thiourea solutions, reducing its environmental impact. Y. A. Akeneev, E. A. Zakharova, G. B. Slepchenko, N.P.Pikula, J. Anal. Chem. 2005, 60, 514.N. Ratnarathorn, O. Chailapakul, C. S. Henry, W.Dungchai,Talanta 2012, 99, 552.