Buletinul tiinţific al Universităţii “Politehnica” din Timisoara, ROMÂNIA Seria CHIMIE I INGINERIA MEDIULUI Chem. Bull. "POLITEHNICA" Univ. (Timioara) Volume 54(68), 1, 2009 18 Studies Regarding the Arsenic Removal from Water C. Muntean * , A. Negrea * , M. Ciopec * , L. Lupa * , P. Negrea * , D. Rosu ** * University “Politehnica” Timisoara, Faculty of Industrial Chemistry and Environmental Engineering, Piata Victoriei, no. 2, 300006 Timisoara, Phone: +40 256 404164, Fax. +40 256 404192, E-mail: petru.negrea@chim.upt.ro ** National Institute of Research-Development for Electrochemistry and Condensed Matter Timioara, România, 300569 Abstract: Arsenic is a naturally occurring element in the Earth's crust that is usually found combined with other elements. Studies have reported that inhalation of arsenic results in an increased risk of lung cancer. Arsenic is released to the environment from a variety of natural and anthropogenic sources. Due to these varieties of pollution sources with arsenic, in the present paper it was studied the possibilities of arsenic removal from water through coagulation-precipitation method using the Jar-Test method. As coagulation-precipitation agents were used Fe 2+ , Fe 3+ and Al 3+ . From the experimental data resulted that the optimum conditions of arsenic removal from water are: reaction mass pH = 9 and a coagulation-precipitation agent dose of 200 mg/L; the best coagulation-precipitation agent is Fe 2+ . Keywords: water, arsenic removal, coagulation-precipitation method 1. Introduction Arsenic is released to the environment from a variety of natural and anthropogenic sources. In the environment, arsenic occurs in rocks, soil, water, air, and in biota. Average concentrations in the Earth’s crust reportedly range from 1.5 to 5 mg/kg. Higher concentrations are found in some igneous and sedimentary rocks, particularly in iron and manganese ores. In addition, a variety of common minerals contain arsenic, of which the most important are arsenopyrite (FeAsS), realgar (AsS) and orpiment (As 2 S 3 ). Natural concentrations of arsenic in soil typically range from 0.1 to 40 mg/kg, with an average concentration of 5 to 6 mg/kg. Through erosion, dissolution, and weathering, arsenic can be released to ground water or surface water. Geothermal waters can be sources of arsenic in ground water. Other natural sources include volcanism and forest fires [1]. Anthropogenic sources of arsenic relate to its use in the lumber, agriculture, livestock, and general industries. Arsenic is emitted as an air pollutant from external combustion boilers, municipal and hazardous waste incinerators, primary cooper and zinc smelting, glass manufacturing, cooper ore mining, and primary and secondary lead smelting. A significant industrial use of arsenic is the production of lead-acid batteries, while small amounts of very pure arsenic metal are used to produce the semiconductor crystalline gallium arsenide, which is used in computers and other electronic applications. Emissions of arsenic from these activities are due to the presence of trace amounts of arsenic in fuels and materials being processed [1-4]. The Environmental Protection Agency from USA classified the inorganic arsenic in the Group A – Known human carcinogenic substances. The classification of arsenic in group A is based on the higher incidence at humans in pulmonary cancer through inhalation and the higher risk of the skin, bladder, liver and lung cancer through drinking water [1,2]. Arsenic ions can be removed from water through various methods [5-14]. The precipitation/co precipitation was the most used method for the arsenic removal from: contaminated waters, including underground water, surface waters and waters from mine sewerage, drinking waters and residual waters from various applications at pilot or industrial scale. This technology can reduce the arsenic concentration at less than 0.05 mg/L and in some cases under 0.01 mg/L. For these reasons in this paper we made studies regarding the arsenic removal from water through coagulation-precipitation method using the Jar-Test method. 2. Experimental For the arsenic removal from water through “Jar-Test” method as coagulation-precipitation agents Al 3+ , Fe 2+ and Fe 3+ were used. The synthetic water containing 100 mg/L arsenic (III) was treated with various doses of coagulation- precipitation agent (100, 200, 300, 400 and 500 mg/L) at various values of the pH of the reaction mass (6, 7, 8, 9, 10 and 11). The pH of the reaction mass was settled either with NaOH 10% or H 2 SO 4 10% solutions. After coagulation, the sample was clarified and then filtered. In the resulted solution was determined the residual concentration of arsenic, iron and aluminum through atomic absorption spectrophotometry, using an atomic absorption spectro- photometer Varian SpectrAA 110. For the establishment of the arsenic removal optimum conditions, it was determined the dependence of the arsenic residual concentration on the pH of the reaction mass, dose of coagulant and on the nature of the used coagulation– precipitation agent.