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Clarifying filters, particularly Auto-Jet Pressure Leaf Filters, are essential in gold and silver processing to remove fine suspended solids before metal recovery. Filter aids enhance filtration efficiency by preventing clogging and improving clarity, allowing for the use of coarser filter media. The integration of these systems in Merrill-Crowe processes ensures consistent operation and optimal recovery of precious metals.

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3 views3 pages

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Clarifying filters, particularly Auto-Jet Pressure Leaf Filters, are essential in gold and silver processing to remove fine suspended solids before metal recovery. Filter aids enhance filtration efficiency by preventing clogging and improving clarity, allowing for the use of coarser filter media. The integration of these systems in Merrill-Crowe processes ensures consistent operation and optimal recovery of precious metals.

Uploaded by

arunbalajibalasubramanian
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We take content rights seriously. If you suspect this is your content, claim it here.
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Clarifying Filters and Filter Aids in Precious Metal Processing

1. Purpose and Importance

In gold and silver processing operations—especially those utilizing the


Merrill-Crowe process—clarifying filters play a critical role in removing fine
suspended solids (e.g., clays, flocs, or colloids) from the pregnant leach
solution before zinc dust precipitation and metal recovery. However, fine
particles, deformable solids, or slimes can quickly blind filter media and
reduce filtration efficiency. This is where filter aids become vital.

2. Clarifying Filters – Auto-Jet System

Auto-Jet Pressure Leaf Filters, typically designed by firms like Whittier


Filtration, are specialized for high-throughput, automated filtration in Merrill-
Crowe systems.

Key Features:

High flux rates and continuous filtration cycles

Removes particles down to 0.5–1 micron

Front-access, no-can design enables easy servicing by a single operator

Integrated sluicing system cleans filter surfaces with high-pressure jets in


under 3 minutes

Filters are automated to switch between active, standby, and cleaning modes

Operation and Design Considerations:

Filtration Capacity: Typically sized for 0.75–0.8 gpm/ft²

Sluicing Flow Rate: Half of process flow (e.g., 500 gpm for a 1,000 gpm
system)

Operating Pressure: Filtration at 55–60 psi; precoat at ~20 psi


No Downtime: Systems often have 3 filters—two in operation, one in
cleaning/precoat cycle

3. Filter Aids – Function and Materials

Filter aids enhance filtration by creating a porous matrix that traps fine solids
before they reach the filter medium, preventing clogging and improving
clarity and flow.

Main Functions:

Prevent filter media blinding

Increase cake porosity and permeability

Allow use of coarser (and faster) filter media while achieving high clarity

Application Methods:

Precoat: A thin uniform layer (0.5–1.0 kg/m²) is applied to the filter medium
before processing begins

Body Feed: A continuous addition of filter aid into the slurry during filtration
to maintain porosity

Common Filter Aid Materials:

DE Usage in Merrill-Crowe Example:

Precoat Slurry: 2% solids applied before filtration

Body Feed Slurry: 5% solids at 0.07 kg/m³

Supplementary Feed: 1.3 gpm of 1% DE per 1,000 gpm of process flow


4. Integration in Merrill-Crowe Systems

The clarified pregnant solution from the filter directly feeds the aeration
tower and then zinc precipitation.

DE helps maintain filtrate clarity and flow, which is essential for efficient
gold/silver recovery.

Precoat and body-feed DE help manage high solids loads, and ensure
consistent operation without unexpected downtime.

5. Summary of Benefits

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