Electroplating wastewater. Wastewater from electroplating and printing plates is classified as acidic or alkaline metal containing wastewater. Therefore the treatment includes methods that neutralize acids and alkali, extract metals, but do not extract organic contaminants. As a result, there is a difficulty to extract metal organic complexes. It should also be noted that certain organic impurities in the electroplating wastewater have enhanced toxicity.
In the copper, nickel and chromium electroplating processes, sulfite-thiocarbamide electrolytes , sulfurol, naphthalene, polyacrylamide, monosaccharides condensation products or polysaccharides, amine derivatives etc are added. These electrolytes produce organic decomposition products that enter the polishing paste.
Research shows that the solution is a closed cycle “etching-regeneration” process in a single stage. At the same time, this wastewater is not properly researched, reliable design and technology, which could extract organic impurities for the reuse of these waters in the same production have not been developed.
The known chemical purification methods include treatment with an oxidizing agent (concentrated acid with a catalyst, ozone, agents containing active chlorine) under normal conditions lead to incomplete oxidation and the chemical oxygen content higher than permissible standards of discharge into sewers. To increase the degree of purification the temperature of the process is raised to120-200°C with the use of aluminum oxide catalysts. The most efficient way with simple equipment design of is direct electrochemical oxidation of organic substances.
It is important to consider that organic substances form complex compounds with metals transferring the metal into complex compounds.
Also worth noting is the impact of organic substances on the chemical recovery process, the nature and concentration of anions in solution.
The analysis of the intensifying factors in the electromagnetic nano-mill (AVS), that have significant effect on wastewater treatment are:
- electrochemical and electromagnetic factors;
- dispersing;
- hydrodynamic factors for intensive mixing.
The electromagnetic nano-mill AVS-100 (laboratory scale) was used in electroplating plant wastewater treatment from heavy metals. The reducing agent used was iron sulfate FeSO4 that reduced hexavalent chromium into trivalent chromium, with introduction of lime milk Ca(OH)2.
In the reaction, 10 mg of 10% iron sulfate solution were added into 0.5 liters of water.
The ferromagnetic particles used for processing were 20 mm long and 1.8 mm in diameter (total weight 200 g). The time for treatment took only 3 seconds.
Table 1 shows the results of removal of heavy metals from electroplating wastewater with electromagnetic nano-mill AVS 100, and a comparison of the original values and maximum allowable concentrations, valid for the European Union.
Table 1
The results of removing heavy metals from electroplating wastewater with electromagnetic nano-mill AVS 100
| № |
Parameters |
Parameter value |
Maximum allowable concentration (European Union) |
|
|
Before treatment |
After treatment |
|||
| 1 |
рН |
1,75 |
6,74 |
6,5-8,5 |
| 2 | Fe, mg/L |
9,7 |
2,77 |
2-20 |
| 3 |
Cu, mg/L |
18,29 |
0,65 |
0,1-4 |
| 4 |
Ni, mg/L |
5,8 |
<0,02 (not detected) |
0,5-3 |
| 5 |
Cr+6, мг/л |
19,08 |
<0,005 (not detected) |
0,1-0,5 |
This study draws the following conclusions:
1) The electromagnetic nano-mill AVS-100 for wastewater treatment from electroplating facilities reduces the concentration of heavy metals to values not exceeding the maximum permissible concentration of the EU, and also achieves complete absence of nickel and hexavalent chromium in the treated water. It shows the promising application of electromagnetic nano-mills in the countries with tough regulations for hexavalent chromium and nickel concentrations in water.
2) Water treatment is instantaneous and saves reagents.
3) Sediment settling is much faster than with a stirring device.