A kind of stainless steel cold rolling pickling wastewater treatment method

Abstract

A method for treating stainless steel cold-rolled pickling wastewater, comprising the following steps: after the pickling wastewater undergoes micro-electrolysis in an iron filings filter and preliminary reduction of hexavalent chromium, it enters a hexavalent chromium secondary reduction tank; the reduced wastewater is neutralized After aeration, it enters the sedimentation tank in the front stage, where the heavy metal sludge is concentrated and dehydrated, and the used iron filings in the iron filings filter are recycled as raw materials for stainless steel smelting; The treated fluoride sludge is used as metallurgical auxiliary materials; after the secondary supernatant continues to interact with the flocculant, it undergoes final precipitation to obtain calcium salt sludge that can be used as building material raw materials; after the acidic wastewater undergoes three-stage precipitation, the final The tertiary supernatant is discharged up to standard after water quality adjustment and sand filtration. The invention has the advantages of low investment, low waste water treatment cost, convenient maintenance, etc., not only can effectively utilize waste iron filings in stainless steel enterprises, but also greatly reduce subsequent waste water treatment costs and operating loads.

Description

Technical field: [0001] The invention relates to a chemical reduction treatment process for heavy metal wastewater, in particular to a treatment method for stainless steel cold rolling pickling wastewater. Background technique [0002] Stainless steel is widely used for its excellent corrosion resistance and good appearance. In the process of annealing, normalizing, quenching, welding, etc., black oxide scales are often formed on the surface of stainless steel, and its composition is mainly NiO 2 , Cr 2 o 3 , Fe 3 o 4 , FeO Cr 2 o 3 , FeO Cr 2 o 3 · Fe 2 o 3 and other dense oxides. This kind of scale needs to be removed by combined processes such as shot blasting, high-temperature alkali leaching, molten salt electrolysis, mixed acid pickling, and multi-stage rinsing. During these surface treatment processes, not only acid regenerated iron powder, turbid circulating water sludge, shot blasting iron powder, iron oxide scale and other iron-containing sludge are pro...

AI Technical Summary

Problems solved by technology

[0005] Considering factors such as mature technology and convenient operation and maintenance, domestic and foreign stainless steel production enterprises mostly combine heavy metal wastewater such as chromium and nickel, fluorine-containing wastewater, mixed acid waste liquid, rinse water and other multiple pickling wastewater into one place to adopt chemical reduction (reduction NaHSO 3 、Na 2 SO 3 , FeSO 4 )-precipitation (the neutralizer is generally milk of lime) method, in order to ensure that the effluent reaches the standard, it is often necessary to add an excessive amount of medicament (often more than 1.5 times the theoretical dosage), HSO in the reducing agent 3 - , SO 3 2- , SO 4 2- The plasma is also neutralized with Ca(OH) 2 The action forms a large amount of CaSO 4 The sedimentation is mixed into the sludge. In this way, the cost of wastewater treatment is high, the output of mixed sludge is large, and the composition is complex, which is difficult to comprehensively utilize. It is recognized as hazardous waste by the state (the number is HW17 in China's National Hazardous Waste Catalog)

For example, the amount of pickling wastewater is 100m 3 / h of a stainless steel plant, regardless of expensive costs such as chemicals, energy consumption, and manpower, the output of mixed sludge alone exceeds 15,000 t / a. Yuan

[0006] Chinese patent CN101096276 discloses a method for extracting chromium and nickel salts in stainless steel pickling wastewater. Although some products containing chromium and nickel salts can be extracted through acid solution leaching, the cost of chemicals in the whole wet process is high, and a large amount of filter residue discharged is difficult. Effective utilization, and the heavy metal concentrate also has the problem of secondary pollution; Chinese patent CN101269889A discloses a treatment method for stainless steel pickling wastewater, which adopts multi-stage reduction and neutralization, the process flow is complicated, and there is waste of repeated addition of acid-base agents. Operational control is difficult, the cost is high, and the sludge classification is not complete, and it is difficult to achieve the purpose of comprehensive utilization

Chinese patent CN1418831A discloses a two-stage method for treating organometallic acidic wastewater. The essence is to separate the neutralization stage from the flocculation stage to overcome the deficiency of one-stage neutralization. The sludge of this technology is still mixed sludge, not only heavy metal sludge It is difficult to separate the mud and calcium salt sludge, and the two sludges of calcium fluoride and calcium sulfate are still mixed together. As a result, it is difficult for both types of sludge to return to the metallurgical process for comprehensive utilization

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