CN1616717A

CN1616717A - Technical treating method for recycling acid washing liquid of sulfuric acid

Info

Publication number: CN1616717A
Application number: CN 200310105509
Authority: CN
Inventors: 张建海
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-11-12
Filing date: 2003-11-12
Publication date: 2005-05-18

Abstract

The technological process of recycling sulfuric acid washing liquid for iron and steel parts can recover all the iron salt and other impurities in low cost. The technological process includes the steps of: exhausting waste acid washing liquid after acid washing, concentration, eliminating impurity, crystallization, returning the mother liquid to the acid washing step and re-compounding the acid washing liquid. The technological process is simple, feasible, relaxed in required apparatus, wide in material source and low in cost, and can save great amount of acid and fresh resource, change impurity into chemical material, reach zero waste liquid drainage and eliminating environmental pollution.

Description

Process treatment method for recycling sulfuric acid pickling solution

The technical field is as follows: the invention relates to a process treatment method for closed-loop recycling of sulfuric acid pickling solution of steel parts, and also relates to a process treatment method for comprehensively utilizing sulfuric acid pickling waste liquid.

Secondly, background art: it is known that steel products must be pickled before being electroplated to remove oil, scale and rust from their surfaces and to clean, smooth and activate the surfaces of the products, so as to obtain a better electroplated layer during electroplating, the pickling solution is usually a sulfuricacid preparation with a concentration of 20-40% and a temperature of I30-60 ℃. The waste liquid obtained after the pickling contains 2 to 4N sulfuric acid preparation and about 2N (about 100g/l) of divalent iron ions, and also contains a small amount of impurities of non-metals such as carbon and arsenic and impurities of heavy metals such as lead, copper, cobalt, nickel, cadmium and manganese (hereinafter, these impurities are collectively referred to as "impurities M"). If the waste liquid is directly discharged, serious environmental pollution can be caused. And a large amount of chemical raw materials are wasted, so that the production cost is increased. It is considered that the process of treating the waste pickling liquid by membrane electrolysis AND the like to recover the iron AND sulfuric acid therein has been proposed abroad to reduce the pollution components during the discharge of the waste water (see the reports of M.WATANALE AND S.Hishimura; U.S. Patnt4, 113, 588; September, 12, 1987 AND U.S. Patnt4, 177, 119; December, 4, 1979; AND the patent of bed assembled to Sotex Research corporation of Japan AND the like), but the process is complicated, the equipment investment is large, the technical requirements are high, a large amount of energy is wasted during electrolysis, AND finally the pollution is eliminated, because the leather has not been reported to be implemented in the above patents, AND the acceptance of China is more difficult. The pollution prevention treatment method generally adopted in China at present is to add a proper amount of lime into waste liquid for neutralization reaction:

the generated precipitate is discharged as waste residue together with the waste liquid. The treatment method can only reduce the pollution degree, and can not eliminate the pollution, wherein a large amount of secondary chemical raw materials are thrown away in vain, become secondary pollution sources, and are not subject to lime, so the production cost of the leather is increased or decreased.

Thirdly, the invention content: the invention aims to provide a process treatment method for recycling sulfuric acid pickling solution, which is cheap, can respectively recover all iron salts and other impurities to be used as secondary chemical raw materials, enables separated sulfuric acid mother solution to form closed cycle of pickling solution, avoids environmental pollution, can save water resources and obviously reduces production cost.

The technical scheme is as follows: the designed process flow sequentially comprises the following steps: discharging pickling waste liquid after pickling, thickening, removing impurities, crystallizing, returning the mother liquid to the pickling process and preparing the pickling liquid again, wherein:

a. concentration increasing process, namely increasing the temperature of the waste liquid to 50-70 ℃, and controlling the concentration of FE2+ in the waste liquid to be increased to 200-250g/l and the concentration of H2SO4 to be uniformly transited from 4N to 0.3 by a method of adding a proper amount of FE (such as scrap iron) in batches;

b. impurity removing step of adding FeS in proper amount while it is hot, stirring and sealing, and separating sulfide precipitate of impurity M generated after chemical reaction from waste liquid (centrifugal separation or negative pressure filtration);

c. a crystallization process, namely cooling the waste liquid to 3-7 ℃, and separating the separated FeSo4 and 7H2O crystals from the mother liquid;

d. returning the mother liquor to the acid washing process and the acid washing solution re-compounding process, returning the treated mother liquor to the acid washing process, adding concentrated H2SO4 in batches, controlling the content of H2SO4 in the mother liquor to be 20-40%, and raising the temperature of the mother liquor to 30-60 ℃ by utilizing the dissolution heat of the concentrated H2SO 4.

The mother liquor thus treated is again subjected to the pickling step.

The principle of the method is that the waste liquid discharged from the pickling process contains 2-4N H2SO4, about 2N (100g/l) Fe2+ and a small amount of impurity M, and the main task of the invention is to effectively separate Fe2+ and the impurity M from the mother liquid as much as possible and separate the separated solid into chemical raw materials with different purposes respectively. The concentration increasing step aims to improve the solubility S of FeSO2&7H2O in the waste liquid so as to improve the concentration of the FeSO2&7H2O in a saturated solution, and the FeSO4&7H2O is precipitated as much as possible during crystallization; another object is to simultaneously reduce the concentration of H2SO4 SO that the impurity M is precipitated as sulfide (M2SY) and separated out before the crystals of FeSO4&7H2O are precipitatedFurthermore, the test shows that the solubility S of H2SO4&7H2O increases with increasing temperature and decreases with increasing FeSO4 concentration in the solution, and the curve is plotted with a larger slope. According to the analysis comparison and verification results of the curve, the temperature of the waste liquid is increased to 50-70 ℃ by heating in the thickening process, and then Fe is added in batches, so that the method is characterized in that (wherein H2 can be recycled), the concentration of Fe2+ in the waste liquid is increased and the concentration of FeSO4 is reduced, So that the process is achieved at the same time, the increase of the temperature and the reduction of the concentration of FeSO4 are both beneficial to increasing the solubility S of FeSO 4.7H2O and increasing the concentration of the saturated solution, and the reduction of the concentration of H2So4 is also beneficial to precipitating the impurity M in the form of MXSY, but tests prove that the concentration of H2SO4 required by various MXSY precipitates is different and is about 0.3-4N, So that the concentration of FE2+ is controlled to be 200-250G/l when Fe is added in batches, and the concentration of H2So4 is controlled to be 0.3N from 4NUniformly mixing, removing impurities, adding appropriate amount of FES to make FES + H2So4+ H2S During operation, proper stirring is required to ensure full and complete sealing, volatilization overflow of H2S is reduced as much as possible, the concentration of FeSO 4.7H 2O is further increased in the reaction, the concentration of FeSO4 is further reduced, MXSY is precipitated one by one, then mother liquor (the stock of impurities M in the waste liquor is very little and reaches 10-4-10-5M) is separated in time from the precipitate and is used as a raw material of a smelting plant after being dried, then the solution enters a crystallization process, namely the temperature of the waste liquor is reduced to 3-7 ℃, the solubility of FeSO 4.7H 2O is greatly reduced, then FeSO 4.7H 2O is precipitated as crystals, and the crystal water accounts for 45.4% in the crystals of FeSO 4.7H 2O, SO the crystals are precipitated, a large amount of solvent water is used for further crystallizing and precipitating FeSO 2.7H O in the waste liquor, while the concentrated crystal water of FeSO 4.4 is obviously increased for promoting FeSO 3873742 and promoting the crystal H4642, the conditions are mutually promoted and complemented, and the temperature reduction crystallization, the concentration crystallization and the same ion effect crystallization are simultaneously combined and mutually promoted, so that the concentration of Fe2 in the waste liquid is quickly reduced to an acceptable degree below 50 g/l. In the process, the concentration of H2SO4 can be increased by 2.5-3 times, the residual MXSY is difficult to precipitate, the linear purity of the separated FESO 4.7H 2O crystal can be ensured to be more than 96%, and the industrial use requirement is completely met. The waste liquid only contains 0.8-3N of H2SO4&7H2O, a small amount of FE2+ and a trace amount of impurity M, and can be used in the acid washing process again. The process is simple and easy to implement,the method has the advantages of low equipment requirement, wide raw material source and low cost, can not only ensure that the pickling solution is recycled by pickling circulation, but also save a large amount of H2SOT and fresh water resources, change impurities into secondary chemical raw materials, realize comprehensive utilization, particularly achieve zero discharge of waste liquid, and eliminate environmental pollution.

Fourthly, the specific embodiment: the present invention will be described in more detail with reference to examples.

The key one of the key points of the invention is the precipitation degree and purity of FESO4&7H2O, because the concentration of H2SO4 and residual MXSY is increased by 2.5-3 times due to the fact that the solution is cooled to 3-7 ℃ once in the scheme, although conditions are not favorable for MXSY precipitation, part of MXSY precipitation is always precipitated along with the FESO4&7H2O, and the purity of the precipitated FESO4&7H2O is greatly influenced and can only reach more than 96%. If it is desired to increase this purity. The crystallization step is preferably carried out in two steps, in the first step, the waste liquid is cooled to 30 to 35 ℃ to crystallize the FESO 4.7H 2O for the first time, and the precipitated FESO 4.7H 2O crystals are separated from the mother liquid. Since the solvent water is still more and the relative concentration of MXSY is still lower, the purity of the precipitated FESO4&7H2O can reach more than 97%, and the high grade can reach more than 98.5% when the recrystallization is carried out once again. And in the second step, the temperature of the waste liquid is cooled to 3-7 ℃ for second crystallization and separation. The obtained FeSO4&7H2O crystal has purity of over 96%. In order to make the acidity of the precipitated FESO 4.7H 2O more satisfactory for use, the solution may be washed with a saturated FESO 4.7H 2O solution until the PH becomes 6, and dried in a room-temperature vacuum drying tank at 20 to 30 ℃ in a vacuum degree of 1 × 104 to 1.5 × 104PA, and then shipped, and the saturated solution for washing may be directly returned to the acid washing step. In the thickening process, for cleanness, easiness and reduction of auxiliary equipment, the waste liquid can be heated by steam, and the temperature of the waste liquid is preferably controlled to be 55-60 ℃, so that energy is not wasted, and cooling is facilitated.

Claims

1. A process treatment method for recycling sulfuric acid pickling liquor is characterized by comprising the following steps: the process flow sequentially comprises the following steps: discharging pickling waste liquid after pickling, thickening to remove impurities, crystallizing, returning the mother liquid to the pickling process and preparing the pickling liquid again, wherein:

a. concentration increasing step, increasing the temperature of the waste liquid to 50-70 ℃, and controlling the concentration of Fe2+ in the wasteliquid to be increased to 200-250g/l and the concentration of H2SO4 to be uniformly transited from 4N to 0.3N by a method of adding a proper amount of Fe in batches;

b. impurity removal process, namely adding a proper amount of FeS while the FeS is hot, properly stirring and sealing, and then separating sulfide precipitate of impurity M generated after chemical reaction from waste liquid;

c. a crystallization step of cooling the waste liquid to 3-7 ℃ and separating the precipitated crystals of FESO4&7H2O from the mother liquid;

d. returning the mother liquor to the acid washing process and the re-preparation acid washing process, returning the mother liquor after the treatment to the acid washing process, adding concentrated H2SO4 in batches, and controlling the dissolution heat of H2SO4 in the mother liquor to raise the temperature of the mother liquor to 30-60 ℃.

2. The process treatment method for recycling sulfuric acid pickling solution according to claim 1, characterized in that: the crystallization process is carried out in two steps, firstly, the waste cold liquid is cooled to 30-35 ℃, the separated crystals of the FESO4&7H2O are separated from the mother liquid, and secondly, the waste liquid is cooled to 3-7 ℃, and the separated crystals of the FESO4&7H2O are separated from the mother liquid.

3. The process treatment method for recycling sulfuric acid pickling solution according to claim 2, characterized in that: the FESO4 · 7H2O crystals precipitated in the crystallization step were washed with a saturated solution of FESO4 · 7H2O to PH 6, and dried in a room temperature vacuum drying tank at 20 to 30 ℃ under a vacuum degree of 1 × 104 to 1.5 × 104PA, and the saturated solution for washing was directly returned tothe acid washing step. A

4. The process treatment method for recycling sulfuric acid pickling solution according to claim 2, characterized in that: in the thickening process, water vapor is adopted to heat the waste liquid, so that the temperature of the waste liquid is controlled at 55-60 ℃.