Dissolution Methods
- Water Dissolution Method
Steps:
Prepare a clean container (e.g., a beaker or mixing tank) and add an appropriate amount of water (it is recommended to use deionized water, distilled water, or tap water; avoid using wastewater, strong acids, strong bases, or water with high salinity).
Start the stirrer to create a vortex in the water, then slowly and evenly sprinkle in the polyacrylamide powder (avoid adding a large quantity all at once, as this leads to clumping).
Continue stirring until the powder is completely dissolved (anionic types typically require 30–60 minutes; non-ionic types require 50–90 minutes; dissolution time should be extended during winter).
Concentration Recommendations:
The general dissolution concentration is 0.1%–0.5% (i.e., adding 1–5 grams of polyacrylamide per liter of water).
For polyacrylamide with a high molecular weight, it is recommended to prepare a lower concentration (e.g., 0.1%) to avoid excessive stirring load or uneven dispersion.
- Accelerated Dissolution Method Using Warm Water
Water Temperature Control: 20–40°C (for anionic types, this range may be extended to 50–60°C; however, temperatures exceeding 60°C must be avoided to prevent the breakage of molecular chains).
Procedure: First, add a small amount of warm water to dissolve a portion of the polyacrylamide; once fully dissolved, add the remaining powder in batches while continuously stirring until the mixture is uniform.
- Pre-dispersion Method
Applicable Scenarios: When the powder is prone to clumping.
Procedure: First, use a small amount of cold water to pre-disperse the polyacrylamide into a paste-like consistency, then add the remaining water and stir until completely dissolved.
Precautions
- Water Quality Selection
Avoid using wastewater, strong acids, strong bases, or water with high salinity, as these water qualities may compromise the dissolution effect or lead to the degradation of the polyacrylamide.
- Temperature Control
The water temperature during dissolution should not exceed 60°C; otherwise, it will accelerate the breakage of molecular chains, thereby reducing the product's effectiveness.
When the water temperature drops below 5°C, the dissolution rate slows down significantly; in such cases, the stirring time should be extended, or warm water should be used for dissolution.
- Stirring Speed and Duration
Maintain a stirring speed between 100 and 300 revolutions per minute (rpm). Avoid excessive speeds, which generate high shear forces that can damage the molecular chains, and avoid speeds that are too slow, which may cause the powder to settle and clump at the bottom. Dissolution Time: Sufficient time is required for dissolution (typically 30 minutes to 2 hours) to ensure complete dissolution with no visible lumps remaining.
- Addition Method
The powder must be sprinkled slowly and evenly into swirling water to prevent the formation of "fish-eyes" (localized, undissolved lumps) caused by adding large quantities all at once.
- Solution Stability and Storage
It is recommended to prepare the solution immediately before use; avoid prolonged storage, which can lead to molecular weight degradation.
- Relationship between Solution Concentration and Storage Duration
0.1% Concentration Solution: Non-ionic types may be stored for up to 7 days, while cationic types should not be stored for more than 24 hours.
3%–5% High-Concentration Solution: These solutions have a longer shelf life but must be diluted prior to use.
- Equipment and Contact Materials
Equipment in contact with the solution (e.g., agitators, piping) should ideally be constructed from stainless steel, plastic, fiberglass, or resin-coated carbon steel to prevent the introduction of iron ions, which can cause chemical degradation.
- Safety Precautions
Polyacrylamide powder may generate dust; therefore, operators should wear masks and gloves during handling. Ensure the workspace is well-ventilated to prevent inhalation of dust particles.
- Type Selection
Select the appropriate ionic type (anionic, cationic, or non-ionic) based on the specific application scenario; avoid mixing different types, as this may result in a loss of efficacy.
- Concentration Adjustment
The actual dosage required should be determined through small-scale laboratory trials to prevent overdosing, which can lead to secondary pollution or unnecessary waste of resources.
