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Removing sediment from the bottom of a mining mixing tank is a high-risk, demanding, and specialized operation in mining and mineral processing plant maintenance. This sediment typically consists of dense, large-particle slurry, is highly abrasive, and may contain toxic reagent residues (such as cyanide). Safely and effectively removing this sediment is critical to maintaining the integrity of the equipment and the safety of operators.
1. Shutdown and Isolation Preparation Procedures
Before any sediment removal operation, strictly following shutdown and isolation procedures is paramount.
1.1 Energy Isolation and Lockout/Tagout (LOTO)
All power sources associated with the agitator must be completely isolated, and the Lockout/Tagout (LOTO) procedure must be implemented:
Agitator Drive: Isolate and lock out the motor power supply to ensure the agitator cannot be accidentally started under any circumstances.
Feed and Discharge Pipelines: Close all feed and discharge valves and implement double block and bleed isolation to prevent upstream slurry or reagents from entering the agitator.
Rinse Water and Reagent Lines: Isolate all connected rinse water and chemical reagent lines and ensure that line pressures are fully depressurized.
1.2 Handling and Monitoring of Toxic and Hazardous Substances
If the mixing tank has been used for cyanide leaching or contains other hazardous chemicals, additional safety measures must be implemented:
Flushing and Neutralization: After draining the slurry, thoroughly flush the interior of the mixing tank with plenty of clean water. Neutralize any remaining cyanide and other toxic substances according to process requirements until the residual concentration is reduced to a safe level.
Gas Monitoring: Before entry, use a professional gas detector to monitor the oxygen content, toxic gases (such as H₂S or HCN), and flammable gas concentrations in the tank to ensure compliance with Confined Space Entry (Confined Space Entry) standards.
2. Professional Technical Methods for Deposits Removal
The sediment removal method should be selected based on the hardness, viscosity, and quantity of the sediment.
2.1 High-Pressure Water Jetting
High-pressure water jetting is the most common and effective method for removing hard or compacted sediments.
Principle and Equipment: A specialized high-pressure water pump generates an extremely high-pressure water stream (typically greater than 10,000 psi) through a nozzle, which cuts, breaks up, and flushes the sediment from the bottom.
Application Characteristics: Suitable for removing tightly compacted hard sediment layers and scaling that is difficult to break up manually. Water jetting must be performed by professionally trained personnel under strict safety regulations.
2.2 Mechanical Breakdown and Manual Cleaning
For loose or semi-solid sediments, a combination of mechanical and manual methods can be used:
Mechanical Breakdown: Where safety permits, use a long-handled tool or pneumatic breaker to initially loosen and break up the sediment, making it easier to pump.
Manual Mucking: Personnel wearing full personal protective equipment (PPE) enter the bottom of the agitator tank and shovel the loosened sediment into the slurry pump intake or transfer it to a dedicated container. This requires a confined space work permit and strict safety monitoring.
2.3 Construction of a Temporary Pumping System
The removed sediment is typically transported to a slurry pond or dedicated treatment facility using a temporary pumping system:
Slurry Pump Selection: A heavy-duty, abrasion-resistant slurry pump must be selected. Its impeller and lining should be made of high-chromium alloy or wear-resistant rubber to handle high solids content and coarse particles.
Pipeline Layout: Temporary pipelines should be made of pressure- and abrasion-resistant materials and securely fastened to prevent leakage or dislodging during transportation.
3. Post-Cleaning Inspection and Restoration
After sediment removal is complete, internal inspection of the agitator tank and system restoration are also part of the professional work.
Internal Inspection: Professionals must conduct a comprehensive inspection of the agitator's lining, impeller, shaft, and baffles, documenting any wear, corrosion, or structural damage to provide an accurate basis for subsequent repairs.
System Restoration: After confirming that there are no personnel, tools, or debris inside the agitator, all LOTO (Loss of Detection) conditions are lifted. The feed, power, and sealing systems are then restored step by step, strictly following operating procedures, to ensure the agitator's safe return to production.
