حذف یون های فلزات سنگین از آب با استفاده از شناور بودن یون Removal of heavy metal ions from water using ion flotation

1. Introduction Excessive use of heavy metals in industries such as leather tanning, metallurgy, petrochemicals, battery and paper manufacturing causes much concern because of their severe threat to human health and the environment [1]. Some of these heavy metals such as Hg (II), As (III), Pb (II), Cd (II) and Cr (VI) are resistant to conventional treatment methods due to strong bonding with organic ligands, which increases their solubility and mobility [2, 3]. This creates problems for public health, since these compounds can be carcinogenic and highly toxic in cellular organisms [4]. Mercury is a volatile heavy metal that has caused public health and environmental concern because of its toxic, persistent, and bio-accumulative properties [5, 6]. Recently, mercury contamination has increased considerably, as it is or has been used for the cathode in the electrolytic production of chlorine and caustic soda, in electrical appliances such as lamps, in industrial and control instruments, namely, switches, thermometers and barometers, in laboratory apparatus and as a raw material for various mercury compounds. Fungicides, antiseptics, preservatives, pharmaceuticals, electrodes, reagents and dental amalgams are other uses [7]. Mercury emissions from human activities is about 30–55% of global atmospheric mercury emissions [8]. Mercury can cause severe neurological and renal disturbances. Short-term or longterm exposure to mercury (inhalation, ingestion or dermal) have toxic effects on the body, mainly the kidneys. Elemental mercury (or metallic), inorganic (to which people may be exposed through their occupation) and organic (e.g., methylmercury, to which people may be exposed through their diet) are the forms of mercury that may result in different degrees of toxicity and effects on the nervous, digestive and immune systems, and on lungs, kidneys, skin and eyes. WHO listed mercury as one of the top ten chemicals or groups of chemicals of major public health concern [9]. The maximum contaminant level of inorganic mercury is reported as 0.002 mg L-1 in water by the EPA. Erosion of natural deposits, discharge from refineries and factories and runoff from landfills and cropland are the main reported sources for inorganic mercury in drinking water [10].