The ion exchange column is a key equipment for purifying high-purity quartz
sand. It adsorbs metal impurities such as Fe ³ ⁺ and Al ³ ⁺ on the surface of
sand particles and in the solution through ion exchange resin (with a required
impurity content of ≤ 10ppm in the finished product), directly determining the
applicability of quartz sand in the fields of electronics and optics. If there
is a rapid decline in adsorption capacity (shortening the service life by more
than 40%) and incomplete removal of impurities (impurities in finished products
exceeding 25ppm), it will lead to a sharp increase in purification costs and
hinder access to high-end markets. Based on the purification characteristics of
ion exchange method and the distribution characteristics of impurities in quartz
sand raw materials, a three-step investigation method is summarized to quickly
restore the equipment's impurity removal performance.
Step 1: Optimize resin selection and filling quality - the core medium
determines the adsorption effect
Poor resin type adaptation, improper loading, or performance degradation are
the main reasons for weak adsorption.
Resin selection mismatch or pollution aging: ordinary strong acidic cationic
resin is selected, which has poor adsorption selectivity for weak acidic
impurities; The resin has been used for more than 8 cycles without regeneration,
and the surface is coated with organic matter (with a pollution level of over
5%), resulting in the failure of active groups; The resin particle breakage rate
exceeds 15%, the specific surface area decreases, and the adsorption capacity
sharply decreases. Replace the quartz sand purification specific chelating
cation resin, which has a 3-fold higher selectivity for metal ion adsorption
than ordinary resin; After each use, check the resin contamination level. If it
exceeds 3%, use a "hydrochloric acid+sodium sulfite" composite cleaning agent
for treatment. The screening and removal rate of damaged resin should be ≥
95%.
Uneven packing density or bed fluctuation: resin packing density below
0.75g/cm ³, excessive bed porosity, solution short circuit leading to
insufficient adsorption; When filling, no bubbles were expelled, resulting in a
"groove flow" phenomenon during operation, and local resin did not participate
in adsorption; The height of the bed is less than 2/3 of the column, and the
contact time is insufficient. According to the process of "layered
loading+gradual compaction", the loading density is controlled at 0.78-0.82g/cm
³, and the bed height is 3/4 of the column; After filling, rinse the bed in
reverse with deionized water to remove any bubbles and ensure that the bed is
uniform and free of gaps.
Step 2: Calibration of operating parameters and feed control - precise
regulation of impurity removal efficiency
Improper feed concentration, flow rate, and solution conditions can
exacerbate adsorption and impurity removal problems.
Imbalance of feeding parameters: quartz sand slurry concentration exceeds
15%, insufficient contact between resin and impurities; The feed flow rate
exceeds 5m/h, the solution stays in the bed for less than 15 minutes, and the
adsorption has not reached saturation; When the pH value of the slurry is below
2, the active groups of the resin protonate and the adsorption capacity
decreases. Control the flow rate to 3-4m/h and the slurry concentration to 10%
-12% through a variable frequency feed pump; Adjust the pH value of the slurry
to 3-4 with dilute sodium hydroxide solution to match the optimal adsorption
conditions of the resin; Install an online concentration detector to monitor the
feed concentration in real-time and avoid instantaneous overload.
Turbulent flow field or abnormal temperature inside the column: blockage of
the water distributor at the inlet of the exchange column, resulting in solution
deviation and local resin overload; When the operating temperature is below 25
℃, the resin adsorption reaction rate decreases by 30%; Above 45 ℃, the thermal
stability of the resin deteriorates and active groups are lost. Disassemble and
clean the water distributor to ensure that the uniformity deviation of the water
distribution is ≤ 5%; Inject constant temperature circulating water into the
exchange column jacket to stabilize the operating temperature at 30-35 ℃,
ensuring adsorption efficiency and avoiding thermal damage to the resin.
Step 3: Optimize the regeneration process and equipment maintenance - extend
the adsorption cycle at the source
Insufficient regeneration agent ratio, operating procedures, and equipment
cleaning can accelerate capacity decay.
Improper regeneration process parameters: The concentration of the
regeneration agent (hydrochloric acid) is below 5%, which cannot completely wash
away the adsorbed metal ions; The regeneration flow rate exceeds 2m/h, and the
contact between the regeneration agent and the resin is insufficient; Incomplete
water washing after regeneration leads to protonation of the resin due to
residual acid solution. Adjust the concentration of regenerant to 8% -10%,
control the flow rate at 1-1.5m/h, and extend the regeneration time to 2 hours;
The water washing stage adopts "gradient washing", with high flow rate first and
then low flow rate, until the pH value of the eluent stabilizes at 6-7 and the
residual acid content is ≤ 0.1%.
Equipment scaling or residual impurities: The thickness of scaling on the
inner wall of the column exceeds 0.5mm (mainly calcium carbonate and silicate),
which affects the flow of the solution; The bottom sieve is blocked, resulting
in uneven pressure on the bed and fluctuations in adsorption efficiency. Soak
the inner wall of the exchange column in dilute hydrochloric acid every month,
remove scaling, and rinse with high-pressure water; Check the bottom sieve every
week, promptly clean the trapped quartz sand fine powder and impurities, and
ensure that the sieve mesh permeability is ≥ 98%.
Daily maintenance should pay attention to: checking the feed concentration,
pH value, and eluent impurity content every day; Calibrate the flow meter weekly
and check the stability of the resin bed layer; Conduct resin performance
testing monthly and optimize regeneration process parameters quarterly. By
taking the above measures, the resin adsorption capacity can be restored to over
90% of the rated value, the impurity removal rate can be increased to 96%, the
impurity content of the finished product can be stabilized within 8ppm, and the
purification cost can be significantly reduced. If there are still problems, it
is recommended to contact the manufacturer to optimize the compatibility between
the resin and quartz sand slurry, and adjust the regeneration process
formula.