The sedimentation characteristics of coal slime water and water hardness

The treatment of coal preparation waste water affecting directly the cleaning effects and economic efficiency is an important step in coal preparation plants. This paper analyses systematically the reasons why the slime water is difficult to clarify and gives the corresponding strategies. The results show that there are a lot of clay minerals which are easy to degrade and low water hardness in some slime water system, which can cause the suspension difficult to clarify. The ions component is affected by many factors in water recycling system, in which the effects of the clay minerals especially kaolinite and montmorillonite are prominent. When the water hardness (Ca2+ or Mg2+ concentration) in the slime water system reaches to the critical hardness, the particles will coagulate, and the slime water clarifies promptly. So the water hardness is the key factor to decide whether the particles settle sown or not. The investigation results of hundreds of coal preparation plants confirm the conclusion.