Laboratory-Scale Apparatus for Semi-Continuous Electrokinetic Dewatering of Phosphatic Clay Suspensions

The by-products of phosphatic clay suspensions are a major waste product of the phosphate mining industry. The phosphate clay suspensions produced from beneficiation are about 130,000 gallons per minute (GPM) at about a solids content of 2 wt%.  After flocculation the settled clay suspensions at 10% solids content are pumped into the clay settling areas (CSAs) for natural settling. This natural clay settling process takes as much as 25 years to reach the demanded value of 40 wt% solids content. Therefore, the CSAs are frequently constructed on the unmined land and currently cover an area of over 100,000 acres in Florida. Disposal of the phosphatic clay suspensions has become the phosphate mining industry’s major challenge. Thus, it is necessary to develop a technique to increase the solids content of the effluent of phosphate clay suspensions from a phosphate mining beneficiation plant and thereby can save the land used for CSAs and recycling water.

 A semi-continuous electrokinetic dewatering apparatus for phosphatic clay suspensions has been designed and its performance has been evaluated. A 2³ factorial design was applied to determine the optimum process parameters. The results show that the electric field was found to have the greatest positive influence on the solids content. The maximum change in solids content reached a plateau as a function of operating time at a given electric field. Moreover, the plateau occurred earlier at larger electric fields, indicating that for the maximum solids content the optimum parameters of the electric field and the operating time can be determined. The CEDA had lower energy consumption and continuously produced the thickened clay which had the highest solid content of about 33 wt%. The CEDA can be operated to cope with dilute initial solids content (3-10%) from a phosphate mining beneficiation plant. The CEDA has potential to replace existing thickening equipment.