http://www.revistadechimie.ro REV.CHIM.(Bucharest)♦69♦No. 3 ♦2018 618 Influence of Different Electroplating Sludge Types on the Iron Ions Recovery Yield MARIA IULIANA MARCUS 1 , MIHAELA ANDREEA MITIU 1 , MARIA VLAD 2 *, MARIANA MINCU 1 , GINA GHITA 1 , ANA MARIA ANGHEL 1 1 National Institute for Research and Development in Environmental Protection - INCDPM Bucharest, 294, Spl. Independentei, 060031, Bucharest, Romania 2 Dunarea de Jos University of Galati, Faculty of Engineering, Domneasca Str., 47, 800008, Galati, Romania Electroplating sludge resulting from wastewater (washing wastewater and technological solutions) treatment is considered to be a hazardous waste, being a mixture of hydroxides of many heavy metals such us: iron, chromium, copper, nickel, cadmium or zinc. The metal compounds from electroplating sludge have a great economic value, thus, a number of techniques have been investigated in order to recover them. This paper presents the results of the research activity in the laboratory in order to recover Fe (II, III, VI) from two types of electroplating sludge: a fresh sludge from wastewaters treatment and an old sludge, stabilized by disposal for many years. Iron recovery was performed by the solubilization of the sludge in several stages, to yield hydroxides or metal salts of chromium, iron, or zinc. The iron recovery has been performed from the cake obtained after the chromium recovery. In this cake, the iron is present in the form of divalent, trivalent and hexavalent iron. The iron recovery yield was 98.50% from fresh sludge (recovery in one stage) and 96.80% from old sludge (recovery in two stages). Keywords: electroplating sludge, iron, recovery yield Treatment and coating processes of metal surfaces require the use of some hazardous substances which are further discharged as washing wastewater and process waste solutions. The process waste solutions that are discharged derived from metal surfaces preparing operations (degreasing, pickling passivating, polishing, etc.) and from the discharge of active washing wastewater (copper, nickel, chrome, zinc or cadmium plating) [1]. The treatment of electroplating wastewater leads to the generation of a sludge that require disposal and is considered a hazardous waste due to the high content of heavy metals in its composition [2]. Among the most hazardous inorganic pollutants for the environment, heavy metals from antropogenic sources play a special role [3]. The pollution with heavy metals represents an important global issue ever since the early 1970s because of their extremely toxic effect even at low concentrations [4]. One of the highest environmental risk is the omnipresence of heavy metals due to their toxicity, persistence and lack of biodegradation [5]. The presence of heavy metals in environment causes toxicity problems. Because of this, even today, these persistent pollutants represent an important issue in Europe [6,7]. However, it can be considered that this type of sludge contain valuable elements, in particular different metals [8]. The electroplating sludge could be reused as material for the extraction of most metals, such as iron, chromium, zinc, etc in order to use them as raw materials [9]. An alternative to use these materials from a hazardous waste is the separation and obtaining of metal salts or metal oxides from sludge in order to recycle them [10]. An iron reach sludge can be found in electroplating industry, where iron comes from pickling and polishing operations of steel and cast iron. The iron extraction in the form of iron oxide allow its use as a potential raw material (pigment) in many industries (ceramics, construction, chemical). This paper presents a study at laboratory scale, by performing a procedure for iron recovery from electroplating sludge. Our interest was focused on the * email: maria.vlad@ugal.ro recovery of valuable iron from different types of electroplating sludge, in order to achieve a recovery yield of metal ions as high as possible. The investigations were carried out in order to specify the correlation between metal ions recovery yield from the electroplating sludge and the age of sludge. Experimental part Two types of electroplatig sludge have been investigated in order to recover the iron ions: A fresh sludge (FS) sampled from a detoxification and neutralization plant (LANCY type) of water and waste solutions from chemical and electrochemical coatings installations. Lancy procedure is a direct method of detoxification and consists of immersing the parts removed from the electrolyte containing toxic substances directly into a neutralizing solution that serves, at the same time, as washing bath [11]. An old sludge (OS) sampled from the decanter of a decommissioned wastewater treatment plant. This sludge is the result of physico-chemical mixed wastewaters treatment derived from various treatment and metal finishing processes (zinc plating, copper plating, cadmium plating, etc.). The sludge is older than 20 years and stabilized by freeze-thaw phenomena and solar activity [12]. The content in metals has been analyzed by atomic absorption spectrometry (AAA), with air-acetylene flame and graphite furnace. The results are showed in table 1. It has been observed a variation of the metal ions content for the two types of investigated sludge. The fresh sludge (FS) derived from wastewater treatment by Lancy procedure, therefore much of the metal ions content was recycled in the treatment process. The process for recovering heavy metals has been consisted in extraction of chromium, iron and zinc by the sludge solubilization in several stages in order to yield hydroxides or metal salts with economic value. Recovered