Process for treating waste pickling liquid of hydrochloric acid by negative-pressure external-circulation evaporation-concentrating crystallization method

Abstract

A process for treating used pickling liquid of hydrochloric acid includes pumping said waste liquid into evaporating chamber, heating it by steam heater while circulating the waste liquid between heater and evaporating chamber, evaporation concentrating to generate ferrous chloride crystal, centrifugal separation to obtain solid ferrous chloride crystal, and returning mother liquid back to waste acid pool. Its advantages are long service life and less leakage of hydrogen chloride.

Description

Technical field [0001] The invention relates to a process for treating waste liquid of hydrochloric acid pickling by a crystallization method. Background technique [0002] Iron oxide will be produced on the surface of steel during rolling. In order to improve the surface quality of steel, it must be pickled. For ordinary steel and general low-alloy steel, sulfuric acid pickling was used in the past. Since the late 1980s, my country has switched to pickling liquid based on hydrochloric acid based on the advanced experience of industrialized countries. After the steel is pickled, a large amount of pickling waste liquid will be produced. At present, nearly one million cubic meters of such waste liquid is discharged every year in the country. It is increasing with the improvement of steel production and quality. This waste liquid contains a considerable amount of residual acid, is also rich in ferrous salts, and contains a small amount of silico-aluminum acid insoluble matter. If it...

AI Technical Summary

Problems solved by technology

FeCl 3 The method is to convert free HCl and FeCl 2 All converted to FeCl 3 , due to FeCl 3 Poor sales and consumption of Cl 2 Now rarely used, FeSO 4 H 2 SO 4 Substitution of FeCl 2 into FeSO 4 , due to FeSO 4 The crystallization temperature is low, and a set of ice machine system needs to be added, and the investment is increased and the operation cost is high

The neutralization method is to neutralize with lime to obtain solid waste residue, which causes serious secondary pollution and waste of resources

The direct roasting method is to oxidize and hydrolyze ferrous salt at high temperature, and evaporate the water to obtain iron oxide and regenerated acid. The high investment and operating costs of this method are unbearable for small and medium-sized enterprises

Atmospheric pressure evaporation concentration crystallization method adopts ordinary two-effect evaporation concentration process. When in use, there are problems of easy blockage of equipment and short service life of equipment.

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