Composite manhole covers feature high load-bearing capacity; the base and cover fit tightly, preventing rocking or rattling and ensuring noise-free operation. They are durable, eco-friendly, lightweight, easy to install and maintain, and can be colored without causing pollution. However, if a composite manhole cover suffers from iron contamination, how should it be treated?
Handling iron contamination in the resin used for composite manhole covers: For resin already contaminated with iron, a soaking treatment using 5%–10% hydrochloric acid is employed. Once the resin is exhausted, the exchanger is drained. For mixed-bed resin, normal regeneration is performed until the anion and cation resins separate; they are then transferred to their respective anion and cation regenerators. A 5%–10% hydrochloric acid solution is added to each exchanger or regenerator, ensuring the liquid level is 20–30 cm above the resin surface. After soaking for 5–10 minutes, compressed air is introduced from the bottom of the vessel for air scrubbing, followed by continued soaking; after another 30 minutes, the scrubbing and soaking process is repeated. This cycle continues until the acidity and iron content of the soaking solution remain essentially unchanged.
For cation resin, normal regeneration is performed using sulfuric acid (H2SO4) at a specific concentration, continuing the acid feed until the inlet and outlet acid concentrations of the cation exchanger or regenerator equalize. For anion double-layer beds, backwashing is first performed to stratify and separate the weak-base and strong-base anion resins; the bed is then displaced with purified water for 30 minutes, followed by normal regeneration using sodium hydroxide (NaOH) solution at a specific concentration, continuing the alkali feed until inlet and outlet concentrations equalize. For mixed-bed anion resin, the resin is first rinsed with purified water for approximately 30 minutes, followed by normal regeneration using NaOH solution at a specific concentration, continuing the alkali feed until the inlet and outlet concentrations of the anion regenerator equalize.
