Settling clay-containing slimes

#This invention relates to a process for separating finely-divided solids that are suspended in an aqueous medium and, more particularly, to a process for treating a colloidal suspension of clay, alone or in combination with other solid materials, to enhance the settling of the solids.

#Clays having a micaceous or platey structure such as bentonite (a montmorillonite clay) acquire the properties of self-suspension, swelling and gelatinizing when they are mixed with water. The clays are advantageously used for these unique properties in many industries. An example of such a beneficial use is in the well drilling industry where bentonite is a component of drilling fluids to suspend the cuttings and carry them out of the well bore.

#These same properties of some clays present considerable problems in other industries when it is desired to remove the clays and other materials from suspension in an aqueous medium. For example, many foundries use a sand washing operation that produces as an undesirable by-product a wash water containing on the order of about 0.2 to about 1.2% by weight of suspended bentonite, carbonaceous material and fine sand. The disposal of this waste product has become a problem in view of recent stringent pollution regulations. The use of standard filtering methods and apparatus for separating the finely-divided material from the waste water before discharging or recycling the water is not entirely satisfactory since the fine suspended particles rapidly blind the filter media.

#The following non-limiting examples are illustrative of the present invention.

#This example illustrates the effect of the process of this invention for flocculating and settling finely-divided material from an aqueous suspension as hereinabove described. The suspension which was utilized in this experiment was a sample of phosphate slimes containing about 4% by weight of suspended solids. Samples of 100 milliliters each of the slime were added to 5 granduated cylinders. A 30% solution of hydrogen peroxide was added to four of the samples in the amounts of 0.025, 0.05, 0.1, and 0.2 milliliter, respectively. No hydrogen peroxide was added to the fifth sample since it was used as a control. The graduated cylinders were each inverted several times to allow thorough mixing and the volume of clear water at the upper portion of each sample was observed and recorded over a 24-hour period. The results of this experiment are given in Table 1.

#Table 1 ______________________________________ TIME 0 0.025 0.05 0.1 0.2 (hours) (mls.) (mls.) (mls.) (mls.) (mls.) ______________________________________ 1.0 6 4 4 20 21 1.5 8 4 26 26 28 2.0 10 10 30 30 31 2.5 11 24 30 31 31 3.0 12 24 30 34 34 4.0 14 24 30 34 36 5.0 16 24 30 36 42 6.0 18 26 30 36 42 7.0 20 28 30 38 42 24.0 25 32 40 43 45 ______________________________________