Aluminum Alloy Anodizing Phosphorus Wastewater Pretreatment System

In the anodizing process of aluminum and aluminum alloys, phosphoric acid is used in the chemical polishing section, resulting in a large amount of phosphorus in the wastewater of cleaning products. There are many studies on the anodic oxidation of aluminum and aluminum alloys to dispose of phosphorus-containing wastewater.

At present, there is a phosphorus removal method for phosphorus-containing wastewater produced in the anodizing chemical polishing process.

First, configure the ferrous sulfate solution.

Take chemically polished phosphorus-containing wastewater, and use alkaline solution to adjust the pH of the wastewater to weakly alkaline.

Then a certain amount of ferrous sulfate solution was added, and the reaction was fully stirred.

After the reaction was completed, PAM was added for flocculation and precipitation.

After solid-liquid separation, the filtrate is discharged, and the filter residue has a high phosphorus content, which can be used as agricultural sludge fertilizer.

The method is simple in process, low in wastewater disposal cost, and low in sludge production from sewage.

The removal rate of low-concentration phosphorus-containing wastewater (TP≤1000ppm) can reach more than 95%, and the removal rate of high-concentration phosphorus-containing wastewater (10000~50000mg/L) can reach 97%.

The invention discloses a preparation method of a process for treating phosphorus-containing aluminum and aluminum alloy anodizing wastewater. The phosphorus content is more than 3000 mg/L, and MgO/Mg(OH)2 slurry is first added to adjust the pH of the wastewater to 5.5-6.5.

Then add PAM for flocculation and precipitation, and then solid-liquid separation is performed to obtain low-phosphorus wastewater with phosphorus content <1000 mg/L.

However, these methods do not make full use of the characteristics of the wastewater itself. The phosphorus and aluminum in the wastewater are pretreated by reacting aluminum ions in the wastewater with phosphate groups in the wastewater and consuming each other.

Instead, phosphorus removal agents such as ferrous sulfate, magnesium hydroxide, PAC, and aluminum sulfate are directly added to the wastewater, resulting in the waste of chemicals. And the corresponding amount of sludge also increased, which failed to fundamentally reduce the operating cost.

Provided are a pretreatment system and method for anodic oxidation phosphorus-containing wastewater of aluminum and aluminum alloys, so as to solve the problems of large dosage of chemicals, large sludge output, and high operating cost in the prior art. The purpose of this invention is to realize through the following technical solutions:

  • Phosphorus-containing wastewater pools where phosphorus-containing wastewater is collected.
  • The outlet of the phosphorus-containing waste water tank is connected to the PH adjustment tank through a pipeline.
  • A sewage lifting pump is arranged in the phosphorus-containing waste water tank, which is used to send the waste water in the phosphorus-containing waste water tank into the pH adjustment tank.
  • There is a liquid caustic feeding port and a pH measuring instrument on the pH adjusting tank.
  • The flocculation tank is equipped with a PAM feeding port.
  • A diaphragm pump is installed on the pipeline between the sedimentation tank and the filter press, which is used to transport the sediment containing a large amount of solid sediment.

Adjust the pH value of the phosphorus-containing wastewater of aluminum anodization to 4.7-6.0, and the preferred pH value is stable at 4.5-5.3, so that aluminum ions and phosphate radicals in the wastewater are removed after generating aluminum phosphate solid particles.

  • The aluminum anodized phosphorus-containing wastewater is transported from the phosphorus-containing wastewater tank to the PH adjustment tank.
  • dd alkaline solution to the pH adjustment tank to stabilize the pH value of the wastewater at 4.7-6.0, and the aluminum ions and phosphate radicals in the wastewater react to form aluminum phosphate solid particles during stirring.
  • Wastewater is sent to the flocculation tank, flocculated with polyacrylamide (PAM) solution, and then sent to the sedimentation tank for precipitation.
  • In the sedimentation tank, the supernatant liquid is discharged as the water treated by the present invention, and the sediment is transported to the filter press by the diaphragm pump for filtration, and the filtrate of the filter press is returned to the phosphorus-containing waste water tank.
  • The lye solution is NaOH aqueous solution and/or KOH aqueous solution with a concentration of 1% to 40%, preferably a concentration of 10% to 30%.

Compared with the prior art, the present invention has the following advantages:

  • Because the pH of the wastewater is less than 2, it is strongly acidic. The applicant found that when the pH was adjusted to 3.4, a small amount of white precipitate was formed in the wastewater. After filtering the precipitate, the phosphorus and aluminum contents in the wastewater were reduced accordingly.
  • When the pH reaches 4.7, the most white sediment is produced in the wastewater. When the pH is higher than 6, the white sediment produced in the wastewater tends to decrease.
  • By filtering out the white precipitation in the wastewater, it is concluded that when the pH is between 4.7 and 6.0, the content of phosphorus and aluminum in the wastewater decreases the most, and the removal rate of aluminum reaches 99% and the removal rate of phosphorus reaches more than 90%.
  • In the process of anodizing aluminum and aluminum alloys, the chemical polishing of phosphorus-containing wastewater has its own characteristics. The phosphorus and aluminum in wastewater are pretreated through the reaction of aluminum ions and phosphate radicals in the wastewater. The sludge output is small, which can reduce the operating cost by 50% to 60%.

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