The deslimer is provided with a central feed box, having a baffled bottom to break the velocity of the inflowing pulp. The bottom, or discharge chamber, has a clear-water inlet, which directs, the flow upward along the axis of the deslimer. The spigot is inserted in a movable holder, attached to the bottom of the discharge chamber, permitting an instant change in the diameter of opening without wetting the operator. Between the feed box and discharge chamber is a valve with sides parallel to the tank and suspended on the vertical center, and which can be raised or lowered by means of a
The concentrate from the flotation section usually contains only 20 to 30% of solids as it leaves the cleaning machine and must be dewatered before being sent to the next department. The operation of dewatering is performed in two stages. First, the bulk of the water is removed in a thickener, from which the concentrate is discharged as a thick pulp ; as a rule the underflow contains 55 to 65% of solids, while 70 to 80% of the original water is recovered in the overflow as a clear liquid. The thickened pulp is then sent to a filter from which the solids are discharged as a cake containing about
As there is seldom enough ground available on which the tailing of a flotation plant can be run to waste without being stacked, it is usual to impound it in some form of dam where the solids can be deposited and the water decanted off for return to the plant. It is generally advisable to recover as much of the water as possible in order not only to save the expense of obtaining a fresh supply but also to return to the flotation circuit any reagents that it still contains in solution. Assuming that it is necessary to return the water to the plant, it is best to dispose of the tailing pulp in
The capacity of a rotary vacuum filter varies from about 200 to 2,000 lb. of dry concentrate per square foot of filtering surface per 24 hours according to the nature of the material and the amount of water that it contains. For the purposes of rough calculations it is usual to assume a capacity of 1,000 lb. per square foot, although this figure is generally exceeded under modern conditions. The moisture in the discharged cake normally ranges from 8 to 12%.
Choosing a Rotary Disk or Drum Filter
The rotary disk filter is the only type capable of handling two concentrates in one machine, the vertical disc construction making it possible
The slime pulp or slurry on leaving the sand classifier with its proper admixture of lime is first led to some form of thickening device if, as is usually the case, the ratio of liquid to solid is too large for economic handling in the cyanide treatment. The form of thickener almost universally used in the early days consisted of a large spitzkasten composed of a number of pointed boxes arranged as a unit in such a way as to give a continuous superficial area.
At the Minas Prietas plant of Chas. Butters and Co., capable of treating 9000 tons of mixed sand and slime tailings per month, the slime
There are two basic types of high rate thickener units:
- Lamina or tube settlers and
- solids recirculation units
They contain space-cutting baffles that intercept settling paths at many levels. Solids settle out onto the baffles and are removed from suspension after settling only a short distance. Where and to the extent that removals are governed by settling rates, such baffles increase the capacity of a space into which they are introduced. They do not increase its volume, so do not increase solids removal where it is governed by flocculation rate and hence by retention time. Thus lamina type units would seem best suited for particulate clarification
Slime treatment, as commonly used by metallurgical engineers, includes thickening, agitation, and filtering and as applied, to cyanidation also includes washing by continuous countercurrent decantation (C.C.D.) and/or filters. “Slime” is the general term used to describe the finer portion of pulp in a combination sand and slime-treatment plant and is usually finer than 100 mesh. The so-called “all-slime” type of plant is that in which all of the ore is ground through a relatively fine mesh such as 100 mesh and where no separate treatment of sand and slime is provided. Equipment
The diaphragm Thickener Underflow Pump is essentially one for low lifts and is particularly adapted to handle metallurgical pulps economically and with minimum attention. The Dorrco diaphragm pump was developed primarily as a means of controlling the density of the underflow from the Dorr thickener in the first continuous treatment of cyanide pulps. It has been proved the most satisfactory method of accomplishing this because of its positive, uniform displacement, which can be regulated at any rate
The concentrate is filtered on two 8 by 10 ft. Oliver filters. One of these filters is used for each roaster. The filter cake discharges onto a conveyor belt which feeds the charge directly to the roaster.
The concentrate filter cake is at best a sticky, puttylike mass. If the moisture exceeds 20 per cent it becomes difficult to handle the cake on the belt and at the charging chute.
The best filtering technique which could be obtained on the 26 per cent sulphur concentrate produced a cake with from 21 to 22 per cent moisture. This was too sticky for continuous use and introduced an excessive amount