Investigation Of Effect Of Heat Treatment On The Flotation Of Turkish Lignites In The Presence Of Monovalent And Bivalent Salts Coals are classified based on their ranks representing the progressive alteration in the natural series from lignite to anthracite. While higher rank coals are inherently hydrophobic, lower rank coals exhibit more of hydrophilic character. For instance, while it is easy to float the bituminous coals, lignite coals need large quantities of collector to become floatable. Poor floatability of low rank coals is generally ascribed to the presence of oxygen containing groups such as carboxyl and hydroxyl groups. It is also known from the literature that flotation of bituminous coal particles in salt solutions in the absence of collector and frother is possible. On the other hand, flotation of lignitic coals is inherently difficult.
The previous studies showed that lower rank coals such as lignite have found to exhibit improved hydrophobicity upon heating. It is also shown that the amount of hydrophobic and hydrophilic groups in coal dictates whether a particular coal is conductive to thermal treatment prior to flotation. The objective of this study was therefore to determine changes in the hydrophobicity of some lignites under modestly controlled heat treatment (105 °C and 150 °C) and correlate the flotation response of lignite coals in the presence of NaCl, KCl, CaCl2, MgCl2 salts without using any flotation chemicals. In addition, several methods such as FTIR, contact angle, zeta potential measurements were used to correlate the flotation response and the quantity of hydrophobicity and hydrophilic groups in coal. For example, FTIR measurements demonstrated a direct correlation between the flotation recoveries and hydrophobic and hydrophilic FTIR peaks in coal. While the use of brine in mineral processing is an essential issue due to lack of fresh water sources in the world, the results obtained from this study help understand the general flotation behavior of minerals in salt solutions.
This study has showed that lignite have found to exhibit improved hydrophobicity upon heating. In addition, several suface chemistry methods such as FTIR, contact angle, zeta potential measurements has used to correlate the flotation response and the quantity of hydrophobicity and hydrophilic groups in coal.
