Water is one of the essential resources for industrial production. Surface treatment and coating production are often the users with large water consumption. How to save water in surface treatment and coating production has been the subject of current research. For example, a foreign aluminum production joint venture daily water consumption of 6300t, of which 30% of surface treatment, in order to save water consumption, the plants are committed to the study of water duplication and recycling problems, the current majority of surface treatment workshop are The degree of different water to do the repeated and recycling, and some plants can do 60% of the water reuse, part of the treated water into the nearby river, part of the fish can be used, after the use of new water treatment technology , The use of new water is greatly reduced, such as a factory surface treatment before l000t / d, now changed to recycling, the new water consumption down to l00t / d.

First, the precipitation and treatment

The wastewater containing the alkali, acid and trace aluminum ions discharged from the washing tank is mixed in the workshop and discharged into the integrated treatment station. The pH value is determined first. If it meets the requirements, it will flow into the multi-stage sedimentation tank. If it does not meet the requirements That is adjusted with acid and alkali. If the acid, with sodium hydroxide for neutralization treatment, aluminum ions in the pH neutral environment to form aluminum hydroxide precipitation. After the suspension of the waste liquid and then polymer coagulant (poly aluminum chloride or polyacrylamide) for agglomeration settlement, separation, the upper part of the clear water, such as environmental protection requirements, can be directly discharged or used. The remaining silt and then dehydrated after delivery, the process is as follows:

1) filled with solution

(1) waste water tank filled with waste liquid

(2) the waste liquid into the neutralization tank

(3) the water into the flocculation tank, concentrator and discharge tank overflow port.

(4) the flocculant dissolved in water and stirring, stirring not more than 5h.

(5) The water is poured into the half of the lye tank and then the same amount of 25% lye is injected.

(6) into the acid tank into the waste acid.

2) Neutral processing

Waste liquid contains more sulfuric acid, need to use NaOH to neutralize, where the reaction is as follows:

Neutralization process to control the pH value in the range of 7 ± 0.5.

3) flocculation sedimentation

The neutralized waste liquid is poured into the agglutination tank and the flocculant is added with stirring. Flocculants use polymer organic compounds, the general use of polyacrylamide, its molecular weight of about l00 million.

The addition of flocculant allows the suspension of Al (OH) 4, flocculation, and then into the sedimentation tank, while stirring precipitation, so that the precipitate and water separation, water from the sedimentation tank edge overflow to the discharge tank, To the outside.

The flocculant injection amount is calculated as follows:

Q2 = 0.7Q1T

Where Q1 - flocculant injection / L · h-1;

Q2 - mud extraction / L · min-1;

T - agglutination time / min.