A simple and efficient process for small-scale cleaning of poorly liberated, difficult-to-wash low-rank coal

ABSTRACT

Low rank coals are often characterized by high amounts of ash forming and sulfur-bearing minerals, poor liberation characteristics, and difficult washability properties. Low-rank coal of Punjab (Pakistan) inherits all these attributes. In this study, the run-of-mine coal sample was crushed down to 9 mm and sieved into six fractions. Coarser fractions were characterized by float-sink test and ultrafine fraction (−0.25 mm) by release analysis. Laboratory-scale shaking table tests were performed on the coarser fractions to evaluate the effects of table tilt and water flowrate on clean coal yield, ash, and sulfur. Likewise, batch flotation tests were conducted on −0.25 mm size fraction to assess the effects of collector dosage, impeller speed, and frother dosage on the same product-quality parameters. Based on the results of these tests and coal-production rate, a low-capacity processing flowsheet was proposed which can generate concentrate and tailing products suitable for cement and brick industry respectively, thus eliminating the requirements of waste disposal. Economic calculations indicate that the mining industry can earn a profit of approximately 60.9 million rupees by processing coal based on the suggested flowsheet.

KEYWORDS:

• Gravity concentration
• shaking table
• flotation
• Punjab coal
• coal cleaning
• coal circuit design