Nano-particulate metal-based emissions from pyrometallurgy and road traffic

Abstract

Anthropogenic activities, as pyrometallurgy and road traffic have plenty of benefits for the society; however they may also pose risks to the environment and human health as well. These risks are mainly connected to the production of wastes during these processes. With iron and steel production the generation and accumulation of fine-grained solid wastes are connected. These solid wastes are partially being recycled and partially they are landfilled. Potential risk of these wastes depends on amounts, chemistry and bioavailability of potentially hazardous metals present in wastes. These metals are persistent and may havesignificant negative impact on living organisms, so their long term presence in the environment may pose significant risks. Non-combustion anthropogenic processes associated with road traffic, such as braking are also known to contribute to the environmental pollution. The friction contact between pad and disc during forced deceleration creates wear debris, which could be divided to the nonairborne and airborne fraction. The non-airborne fraction may settle on brake hardware, road surfaces, and in the vicinity of roads. These particles are considered to be large, but their surface may be “covered” with attached ano-sized particles, which can be potentially released to the environment. Aim of the thesis was to evaluate the mobility of the nano-sized particles in the water environment and their morphology and chemistry characterization from five selected pyrometallurgical sludges (blast furnace sludge, blast furnace sludge treated in hydrocyclone overflow and underflow, tandem furnace sludge, and oxygen converter sludge), and nonairborne wear debris from two model brake pads (G6C and G6C/KATI), and two commercial brake pads (SMP1 and SMP2). Scanning electron microscopy, X-ray powder diffraction, FTIR spectroscopy, and Raman microspectroscopy were used for characterization of initial samples. According to European standard the suspensions were prepared from pyrometallurgical sludges. Also the sedimentation technique was used for suspension preparation of pyrometallurgical sludges and brake wear debris. Prepared suspensions were dried on a glass slide and characterized by scanning electron microscopy and Raman microspectroscopy. Transmission electron microscopy measurements were evaluated with liquid suspensions. These analytical techniques revealed presence of nano-sized metal based and some crystalline particles. Filtered aqueous leachate is inaccurately considered homogenous.