Merrill-Crowe Plants,
10 GPM & 50 GPM



310 830 6601
Fax: 310 830 9336


Sepor manufactures Merrill-Crowe Plants for the recovery of gold and silver from cyanide solutions.

Two primary pilot plant sizes are manufactured, a 10 gallon per minute plant (65 tons of solution per day), and a 50 gallon per minute plant (300 tons of solution per day). The plants are complete and include solution circulation pumps, flow meter for plant feed, de-aeration system with vacuum pump, de-aeration tower level control with recirculation system, precipitation pre-coat filter, clarifying pre-coat filter, zinc dust hopper, zinc dust feeder, instrumentation, internal piping, steel mounted frame. All plants are for continuous operation. All that is necessary for the user to supply is piping to and from the unit, external wiring to the unit and site installation.

The standard configuration of the Portable Merrill-Crowe Plant uses canister pre-coat type filters for clarifying and precipitation filters. Plate and frame filters are available for precipitation filter, as an option. The dimensional size of the plant is increased when adding the plate and frame filter by approximately 3′ x 6′.



50 GPM (300 TPD) M/C Plant

Catalog Number Plant Size Shipping Volume (Ft.3) Shipping Weight (Lbs.)
050M-002 65 Tons/Day (10 GPM) 135 1,200
050M-005 300 Tons/Day (50 GPM) 300 3,100


Mine Annual Production
Ore Average
Au (g/Mt)
Shipping Weight (Lbs.) Average recovery from leach (%) Preg Solution Flow Rate, Ltr/Min Solution Assay,
Au (PPM)
Solution Assay, Ag (PPM) Au Annual Produc-tion (Kg) Ag Annual Produc-tion (Kg) Recovery Method Merrill-Crowe Efficiency
Merrill-Crowe Efficiency Silver
State of Maine 450,000 0.5 34.3 0.8 680 0.5 15 158 4631 SOM MC 88.41% 86.38%
C-1 1,800,000 0 108 0.8 9085 0 26 0 81,000 MC NA 95.25%
T-1 90,000 0.69 60 0.8 870 0.3 13 31 2,177 MC NA 89.11%
Z-1 3,270,000 1.03 0 0.8 4921 2 0 2177 0 MC 76.80% NA
The table above illustrates the typical efficiency range experienced by Merrill-Crowe Plants operating in mills. This data was obtained from the now defunct US Bureau of Mines, and involved a study of heap leach mining, carbon absorption and zinc precipitation of precious metals during the period 1980 to 1990. It correlates well with the general rule of thumb, that recoveries from a Merrill-Crowe Plant can range from 70% to 95%. There are many interfering elements. Such as the non precious metal components in the ore, the elements dissolved in the process water, the variance of the ore from day to day, etc..


Above is a graph of plant volume processed versus the solution content of precious metals for cyanide leach of gold and silver. Generally, when the data are to the right of the curve, it might tend to favor a Merrill Crowe Plant, while to the left of the curve, it might tend to favor a carbon adsorption system for recovering the precious metals from the solution. Obviously, there is more to consider in such a decision, but this will generally hold true, and at least indicate one or the other should be considered.

Historical Info On Gold and Cyanide

The discovery that gold was soluble in weak solutions of potassium cyanide (mid 19th century) presented a major tool to gold miners, who could now dissolve the gold in the ore and discard the waste rock. Modern cyanide plants typically use a cyanide solution of 0.05% NaCN to dissolve gold from the ore. Following the discovery of gold’s solubility in cyanide, it was discovered that passing the gold dissolved in cyanide solu- tion through chips of zinc caused a gold to precipitate. The zinc reacts with the cyanide, and releases the gold as a solid precipitate. Early zinc precipitation systems simply used a wooden box filled with zinc chips. These systems worked, however, they were very inefficient, recovering about 30% of the precious metal, since much of the dissolved gold still remained in solution after passing through the zinc box. The discovery that zinc was much more efficient in reacting with a Au-Ag-CN solution when most of the dissolved oxygen was removed, resulted in the Merrill- Crowe process. Merrill-Crowe plants were the first use of the zinc precipitation process that made the use of zinc a highly efficient gold recovery process. Primarily, the Merrill-Crowe process works so much better than the early zinc boxes because in order for efficient and complete precipitation of gold and silver from a cyanide leach solution to occur, dissolved oxygen must be removed from the solution. A Merrill-Crowe plant typically reduces the oxygen content of a cyanide solution to about 1 PPM or less.

The product from a Merrill Crowe Plant may be fluxed and melted, poured into dore bars, redissolved in cyanide and electrowinned as a higher purity gold product, then melted and poured into dore bars, or sent to a refiner for 99.9 salable gold bars.

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