A method for recovering zinc chloride from galvanized steel scrap

Abstract

The invention discloses a method for recycling zinc chloride from galvanized scrap steel, and the steps include: sorting treatment, pretreatment, first rinsing treatment, corrosion inhibition and dezincification treatment, second rinsing treatment, material cutting treatment, composite impurity removal treatment and evaporation treatment. The invention adopts a multi-step method of wet dezincification and oxidation, zinc powder reduction, and distillation concentration to achieve short-process zinc-iron separation and direct recovery of all zinc resources, and has a short-process treatment process with obvious iron suppression, zinc dissolution, and no non-zinc impurities introduced. The synergistic effect of multi-step and step parameter control realizes the complete and effective separation of zinc and iron and the acquisition of high-concentration zinc chloride dezincification liquid, and realizes the direct recovery of zinc resources while realizing the short-process wet separation of zinc and iron, ensuring the quality reliability and stability of galvanized scrap steel added as furnace charge in steel smelting enterprises, and is conducive to the purity of raw materials for recycling galvanized scrap steel as furnace charge.

Description

Technical Field

[0001] The present application relates to the field of recycling and utilization of scrap steel materials, and in particular to a method for recycling zinc chloride from galvanized scrap steel materials. Background Art

[0002] The zinc coating on the steel substrate is an anodic coating in general corrosive media. It not only acts as a barrier layer for the substrate, but more importantly, it can play an electrochemical protective role. So far, galvanizing is still the most effective method for steel surface corrosion protection. At present, about 30% of the total annual global steel production adopts galvanizing for corrosion protection. With the continuous development of the steel industry and the replacement application of new high-corrosion-resistant materials, hundreds of millions of tons of scrap steel are generated every year. Scrap steel is an indispensable raw material for the modern steel industry and the only green energy carrier and sustainable development renewable resource that can replace iron ore in large quantities. In recent years, the proportion of galvanized scrap steel in scrap steel has increased year by year, and it shows an accelerating trend. Galvanized scrap steel is a valuable resource that can be recycled. Galvanized scrap steel contains iron and zinc, and its recycling has significant economic and environmental benefits. However, in the current scrap steel recycling process, galvanized scrap steel is still simply treated the same as scrap steel, and is collected, sorted and packaged before being handed over to steel smelting enterprises as furnace charge. A large amount of production practice has proved that galvanized scrap steel enters the furnace dust along with the zinc brought into the furnace charge system, and is easily enriched in the blast furnace after sintering, causing nodules, which has serious harm to the blast furnace production process. For this reason, various steel companies control the allowable value of blast furnace zinc load below 0.5Kg / t, while the zinc content in galvanized scrap steel is far higher than this threshold. In order to prevent zinc from entering the steel smelting process and effectively separate and utilize zinc in galvanized scrap steel, people have carried out research on methods for dezincification of galvanized scrap steel, such as mechanical method, alkaline leaching electrolysis method, pyrolysis method, etc.

[0003] With the continuous improvement of my country's infrastructure and the end of the service life of traditional galvanized steel products, the amount of galvanized scrap steel in my country has been increasing year by year. Therefore, the separation of zinc and iron and the recycling of galvanized scrap steel have become urgent problems to be solved in the steel smelting industry and metal recycling field. In response to this, industry workers have continuously innovated in the mechanical method, alkaline leaching electrolysis method, and pyrometallurgical method for separating zinc from galvanized scrap steel.

[0004] The literature (Study on new technology of removing abandoned tobacco zinc platecoating by using mechanical method. Advanced Materials Research, 2012, 472: 2944-2947) uses a mechanical method to remove the zinc layer on the surface of waste galvanized sheet. The zinc removal rate can reach 98% while ensuring the allowable roughness. However, the samples in the literature are regular galvanized sheets, and the separation and recovery of the removed zinc is not mentioned.

[0005] The literature (Dezincing of zinc alloy coated steel scrap in hot caustic soda. Steel Research, 1999, 70(6): 227-232) uses alkaline electrolysis to remove the zinc layer on the surface of hot-dip galvanized steel scrap, analyzes the influence of alkaline immersion parameters, and also points out the defects of the long process of alkaline electrolysis.

[0006] In response to the problems of mechanical and alkaline leaching and electrolytic dezincification, researchers have proposed a technical idea for pyrometallurgical dezincification of galvanized scrap steel, which involves heating in air or vacuum, inert gas, or reducing atmosphere in a heating furnace to separate zinc and iron by utilizing the difference in their vaporization temperatures; or combining acid washing and alkaline leaching for dezincification.

[0007] Publication No. CN111733333A discloses a method for dezincifying galvanized scrap steel. The technology mixes galvanized scrap steel with coke powder in a certain mass ratio, then introduces inert gas into a rotary kiln and heats to 900-1050°C for pyro-dezincification, so that the galvanized layer can be effectively recovered. Although the technical solution controls the oxidation of the separated zinc to a certain extent, the technical solution also has the disadvantages of high energy consumption and low efficiency, and it is difficult to meet the processing requirements of large quantities of galvanized scrap steel. At the same time, there are many impurities in the zinc after separation, and subsequent impurity removal treatment is required.

[0008] Publication No. CN218507876U discloses a device for recycling zinc from galvanized steel scrap and zinc-containing materials. The core of this technology is to disclose a crushing device for galvanized steel scrap, which can crush large-sized galvanized steel scrap and improve the efficiency of pyro-zinc removal. In essence, it still adopts pyro-zinc removal and still does not solve the problems existing in pyro-zinc removal.

[0009] Publication No. CN113909255A discloses a galvanized scrap steel dezincification device, the core technology of which is to stir the crushed galvanized scrap steel and further crush it to increase the dezincification rate.

[0010] Publication No. CN107500340A discloses a method for recycling zinc in galvanized scrap steel and zinc-containing materials. Its technical solution is to first pickle the galvanized scrap steel and zinc-containing materials, add hydrogen peroxide to oxidize, and add strong alkali to remove impurities; add sodium carbonate solution to precipitate zinc carbonate; add sodium hydroxide solution to precipitate zinc hydroxide; roast the precipitated zinc carbonate or zinc hydroxide to obtain high-purity active zinc oxide. Its core technology belongs to the acid-washing and alkali-leaching method in principle, using acid to convert the zinc on the surface of the galvanized scrap steel substrate into zinc ions, and then using sodium bicarbonate and sodium hydroxide to convert the zinc ions into alkaline precipitates, and then roasting at high temperature to convert them into zinc oxide, so as to realize the conversion and recycling of zinc on the surface of the galvanized scrap steel into zinc oxide. It is easy to judge from its process flow that its consumption of strong acid and strong alkali is large, and the process flow is long, and it is difficult to mass produce in terms of processing cost and operation.

[0011] Publication No. CN116287717A discloses a zinc-containing scrap steel dezincification and recovery device and a method of use, the device comprising: a track feeding unit comprising a weighing component, an inlet track and an outlet track, the zinc-containing scrap steel is transported to the inlet track; a weighing component is arranged under the inlet track; the dezincification unit comprises a bearing component, a heating component, a vibrating component, a purging component and a zinc collecting component, the bearing component is built of refractory materials in an upper and lower cone shape, the outlet track passes through the bearing component and extends to one side, a heating component is arranged at the front end of the inner side of the bearing component and is located above the outlet track, and a layer of steel plate is added to the inner wall; a purging component is arranged on the inner wall of the outlet side of the bearing component to spray argon gas on the scrap steel; a vibrating component is arranged at the bottom of the outlet track, and the zinc layer is accelerated to separate from the surface of the scrap steel by vibration. Its technical core still belongs to pyrometallurgical dezincification, but it is a dezincification that is completed continuously on a moving track by introducing argon gas and assisting vibration.

[0012] Publication No. CN115342633A discloses a composite rotary kiln and a light and thin scrap steel degreasing and dezincification recovery system and method, wherein the composite rotary kiln comprises a rotary kiln cylinder, wherein the rotary kiln cylinder comprises an inner heating kiln section, an oxidation kiln section and an outer heating kiln section which are sequentially arranged and interconnected, and the light and thin scrap steel degreasing and dezincification recovery system comprises a scrap steel crushing system, a preheating vertical furnace, an induced draft fan, a one-shot hot forging system and a dust removal and fume exhaust system. The core of the system is still pyrometallurgical dezincification, and it is dezincification after the galvanized scrap steel is crushed. Summary of the invention

[0013] The purpose of the invention is to provide a method for recovering zinc chloride from galvanized scrap steel, which can achieve short-process zinc-iron separation and direct recovery of all zinc resources.

[0014] Technical solution: The method for recovering zinc chloride from galvanized steel scrap according to the present invention comprises the following steps:

[0015] Step 1, sorting and processing, according to whether the galvanized scrap steel has a paint coating on its surface, to divide it into bare galvanized scrap steel and galvanized scrap steel with a paint film on its surface;

[0016] Step 2, pre-treatment, cleaning the surface of the galvanized steel scrap according to the surface state of the sorted galvanized steel scrap, removing surface grease, paint film residues and dirt;

[0017] Step 3, performing a first rinsing treatment, immersing the pretreated galvanized scrap steel in rinsing water for a first rinsing;

[0018] Step 4, performing corrosion inhibition and dezincification treatment, immersing the galvanized scrap steel after rinsing treatment into a dezincification solution in a dezincification tank, wherein the dezincification solution is a pickling solution with a corrosion inhibitor added thereto, removing the zinc coating on the surface of the galvanized scrap steel through a solution reaction, and detecting the content of zinc ions in the dezincification tank in real time online;

[0019] Step 5, performing a second rinsing treatment, rinsing the scrap steel substrate after corrosion inhibition and dezincification with rinsing water for a second time to remove the residual zinc ions on the surface of the steel substrate;

[0020] Step 6, cutting the scrap steel substrate after the second rinse into a suitable size or structure for easy subsequent packaging or briquetting;

[0021] Step 7, performing a composite impurity removal treatment, when the zinc ion content in the dezincification tank is within a set zinc content threshold range, performing continuous treatments of oxidation precipitation, first filtration, zinc powder reduction and second filtration on the dezincification liquid in the dezincification tank, and performing online detection of the zinc ion content;

[0022] Step 8, performing evaporation treatment, heating and evaporating the dezincification liquid after the composite impurity removal treatment at a set temperature in an evaporator to obtain a zinc chloride aqueous solution or zinc chloride crystals.

[0023] Furthermore, in step 2, when performing surface cleaning, if the galvanized scrap steel is a paint film galvanized scrap steel with a paint coating on the surface, a paint stripping cleaning method is adopted; if the galvanized scrap steel is a bare galvanized scrap steel without a paint coating on the surface, an alkali washing method is adopted.

[0024] Furthermore, the alkaline cleaning method is to use a weak alkaline cleaning solution and assist with ultrasonic cleaning; the paint stripping cleaning method is to use a neutral solvent-type paint stripping cleaning solution and assist with ultrasonic cleaning.

[0025] Furthermore, in step 4, the mass percentage of the corrosion inhibitor added to the pickling solution is 0.8-1.5%.

[0026] Furthermore, in step 5, during the second rinsing, the scrap steel substrate is rinsed 1 to 2 times with rinsing water.

[0027] Furthermore, in step 7, the zinc content threshold range is 185 g / L to 195 g / L.

[0028] Furthermore, in step 7, when the oxidation precipitation treatment is performed, hydrogen peroxide is used for oxidation treatment. During the oxidation treatment, the pH value of the dezincification solution is maintained between 3.5 and 4, and the pH value is maintained by adjusting hydrogen peroxide or hydrochloric acid.

[0029] Furthermore, in step 7, when the zinc powder reduction treatment is performed, the amount of zinc powder added is 50 g to 100 g per cubic meter of the dezincification liquid.

[0030] Further, in step 8, the zinc chloride mass content in the zinc chloride aqueous solution is not less than 50% and Fe 2+ The mass content is not higher than 0.02g / L~0.5g / L.

[0031] Furthermore, in step 8, the mass content of zinc chloride in the zinc chloride crystals is not less than 95%.

[0032] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention adopts a multi-step method of wet dezincification and oxidation, zinc powder reduction, and distillation concentration for galvanized scrap steel, thereby realizing short-process zinc-iron separation and direct recovery of all zinc resources. The short-process wet dissolution zinc-iron separation method adopts a short-process treatment process with obvious iron suppression, zinc dissolution, and no non-zinc impurities introduced. The synergistic effect of the multi-step and step parameter control realizes the complete and effective separation of zinc and iron and the acquisition of high-concentration zinc chloride dezincification liquid, and realizes direct recovery of zinc resources while realizing short-process wet separation of zinc and iron; (2) The galvanized scrap steel treatment method of the present invention includes a multi-step treatment of sorting, classification pretreatment, corrosion inhibition dezincification, and rinsing. The multi-step parameter control and treatment synergistic effect realizes the separation of zinc and iron while realizing no zinc residue on the surface of the scrap steel, thereby ensuring the quality reliability and stability of the galvanized scrap steel added as furnace charge in steel smelting enterprises, and is beneficial to the purity of the raw materials for recycling the galvanized scrap steel as furnace charge. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The figure is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0034] The embodiments of the present application will be described in more detail below with reference to examples. Although the embodiments of the present application are shown in the examples, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present application more thorough and complete, and the scope of the present application can be fully communicated to those skilled in the art.

[0035] It should be noted that the specific equipment and methods for related detection and testing involved in this application are as follows, which can be fully understood by those skilled in the art:

[0036] The Zn content in the dezincification solution was analyzed using the ICPS-1000Ⅱ inductively coupled plasma atomic emission spectrometer (ICP-AES) produced by Shimadzu, Japan. 2+ Concentration and Fe 2+ Concentration. During the test, the test solution is quantitatively diluted to an appropriate concentration, and finally the zinc chloride and Fe in the test solution are converted according to the test results and the dilution multiple. 2+ content.

[0037] The thickness of the galvanized layer of galvanized scrap steel is tested by magnetic thickness gauge. The test samples are randomly selected from the same batch of galvanized scrap steel, and 5 different points on the surface of the sample coating are measured, and the average value is calculated. Refer to GB / T4956-2003 / ISO 2178:1982 "Magnetic method for measuring the thickness of non-magnetic coatings on magnetic metal substrates".

[0038] Use a commercially available pH test pen to test the pH value of the solution.

[0039] like Figure 1 As shown, the method for recovering zinc chloride from galvanized steel scrap disclosed in the present invention comprises the following steps:

[0040] Step 1, sorting and processing, according to whether the galvanized scrap steel has a paint coating on its surface, to divide it into bare galvanized scrap steel and galvanized scrap steel with a paint film on its surface;

[0041] Step 2, pretreatment, according to the two surface states of the galvanized steel scrap after sorting, respectively clean the surface of the galvanized steel scrap, remove surface grease, paint film residues and dirt, if the galvanized steel scrap is a paint film galvanized steel scrap with a paint coating on the surface, then adopt a paint stripping cleaning method, if the galvanized steel scrap is a bare galvanized steel scrap without a paint coating on the surface, then adopt an alkali cleaning method, the alkali cleaning method is to use a weak alkaline cleaning solution and assist with ultrasonic cleaning, the paint stripping cleaning method is to use a neutral solvent-type paint stripping cleaning solution and assist with ultrasonic cleaning;

[0042] Step 3, performing a first rinsing treatment, immersing the pretreated galvanized scrap steel in rinsing water for a first rinsing;

[0043] Step 4, performing corrosion inhibition and dezincification treatment, immersing the galvanized scrap steel after rinsing treatment into a dezincification solution in a dezincification tank, wherein the dezincification solution is a pickling solution with a corrosion inhibitor added thereto, removing the zinc coating on the surface of the galvanized scrap steel through a solution reaction, and detecting the content of zinc ions in the dezincification tank online in real time, wherein the mass percentage of the corrosion inhibitor added to the pickling solution is 0.8 to 1.5%;

[0044] Step 5, performing a second rinsing treatment, rinsing the scrap steel substrate after corrosion inhibition and dezincification with rinsing water for a second time, rinsing the scrap steel substrate with rinsing water for 1 to 2 times to remove the residual zinc ions on the surface of the steel substrate;

[0045] Step 6, cutting the scrap steel substrate after the second rinse into a suitable size or structure for easy subsequent packaging or briquetting;

[0046] Step 7, performing a composite impurity removal treatment, when the zinc ion content in the dezincification tank is within the set zinc content threshold range, the dezincification liquid in the dezincification tank is continuously treated with oxidation precipitation, first filtration, zinc powder reduction and second filtration, and the zinc ion content is detected online, the zinc content threshold range is 185g / L to 195g / L, and the preferred value is 190g / L. When performing the oxidation precipitation treatment, hydrogen peroxide is used for oxidation treatment. During the oxidation treatment, the pH value of the dezincification liquid is maintained between 3.5 and 4, and the pH value is maintained by adjusting hydrogen peroxide or hydrochloric acid. When performing the zinc powder reduction treatment, the amount of zinc powder added is 50g to 100g per cubic meter of the dezincification liquid.

[0047] Step 8, performing evaporation treatment, heating and evaporating the dezincification liquid after the composite impurity removal treatment in an evaporator at a set temperature to obtain a zinc chloride aqueous solution or zinc chloride crystals, wherein the zinc chloride mass content in the zinc chloride aqueous solution is not less than 50% and Fe 2+ The mass content is not higher than 0.02g / L-0.5g / L, and the mass content of zinc chloride in zinc chloride crystals is not less than 95%.

[0048] Embodiment 1:

[0049] Categories of galvanized scrap steel to be recycled: Several scrap galvanized two-wave steel guardrail plates, material Q235B, average thickness of the galvanized layer 97μm.

[0050] Step 1: Detect a very small amount of concrete blocks mixed in the steel guardrail plate;

[0051] Step 2, immersing 2 tons of the steel guardrail panels sorted in step 1 in a first pretreatment tank at room temperature, wherein the pretreatment solution in the first pretreatment tank is a weak alkaline solution with a pH value of 9, and performing ultrasonic-assisted cleaning for 5 minutes;

[0052] Step 3, immersing and rinsing the steel guardrail plate treated in step 2 in a first rinsing tank at room temperature;

[0053] Step 4, immersing the steel guardrail plate treated in step 3 into a corrosion-inhibiting dezincification solution prepared by hydrochloric acid, wherein the initial pH value of the corrosion-inhibiting dezincification solution is not greater than 1, and a hexamethylenetetramine corrosion inhibitor with a mass fraction of 0.8% is added to the dezincification solution, and the dezincification time is extended by 3 minutes until bubbles visible to the naked eye just disappear on the surface of the steel guardrail plate;

[0054] The steel guardrail plates are processed in steps 1 to 4 in a batch of 3 tons each, and multiple batches are cyclically processed. When the pH value of the corrosion-inhibiting dezincification solution is greater than 5, industrial hydrochloric acid is added to the dezincification solution to adjust the pH value of the corrosion-inhibiting dezincification solution to less than or equal to 1;

[0055] When the zinc ion online detection system detects that the zinc ion content in the corrosion-inhibiting dezincification liquid is 187 g / L, the corrosion-inhibiting dezincification liquid is pumped into the treatment tank in step 7, and the standby dezincification tank starts to work;

[0056] Step 5, immersing the dezincified steel guardrail plate in step 4 into a third rinsing tank at room temperature for rinsing once, and then immersing it into a fourth rinsing tank for rinsing once;

[0057] Step 6, cutting, truncating, packing, and briquetting the steel guardrail panels rinsed in step 5, and storing them for sale;

[0058] Step 7, adjusting the pH value of the dezincification liquid pumped in step 4 to 3.5 with industrial hydrochloric acid, adding hydrogen peroxide to the dezincification liquid and assisting stirring, then standing and settling, filtering and pouring the trough, adding zinc powder in an amount of 80g / cubic meter to the dezincification liquid in the trough and assisting stirring, then standing and settling, filtering and pouring the trough, and adding industrial hydrochloric acid to the dezincification liquid in the trough to adjust the pH value to 3.5;

[0059] Step 8, the dezincification solution treated in step 7 is pumped into an evaporator, kept at 260°C for 4 hours, and cooled to obtain a concentrated zinc chloride solution; ICP-AES detection and calculation show that the zinc chloride content in the concentrated zinc chloride solution is 51.26%, and the Fe content in the concentrated zinc chloride solution is 2.3%. 2+ The content is 0.0098g / L.

[0060] 1 kg of the steel guardrail plate from step 6 was cut and completely dissolved with analytical pure hydrochloric acid. The zinc content in the steel guardrail plate was determined and calculated by ICP-AES. The zinc content was 2.1×10 -6 g, indicating that the steel guardrail plate in step 6 contains almost no zinc.

[0061] Embodiment 2:

[0062] Categories of galvanized scrap steel to be recycled: Several scrap galvanized two-wave steel guardrail plates, material Q235B, average thickness of the galvanized layer 114μm.

[0063] Step 1, detect a very small amount of concrete blocks mixed in the waste galvanized steel guardrail plate;

[0064] Step 2, immerse 3 tons of the steel guardrail panels sorted in step 1 in a first pretreatment tank at room temperature, wherein the pretreatment solution in the first pretreatment tank is a weak alkaline solution with a pH value of 10, and perform ultrasonic-assisted cleaning for 3 minutes;

[0065] Step 3, immersing and rinsing the steel guardrail plate treated in step 2 in a first rinsing tank at room temperature;

[0066] Step 4, immersing the steel guardrail plate treated in step 3 into a corrosion-inhibiting dezincification solution prepared by hydrochloric acid, wherein the initial pH value of the corrosion-inhibiting dezincification solution is not greater than 1, and a hexamethylenetetramine corrosion inhibitor with a mass fraction of 1.5% is added to the dezincification solution, and the dezincification time is extended by 3 minutes until bubbles visible to naked eyes just disappear on the surface of the steel guardrail plate;

[0067] The steel guardrail plates are processed in steps 1 to 4 in a batch of 3 tons each, and multiple batches are cyclically processed. When the pH value of the corrosion-inhibiting dezincification solution is greater than 5, industrial hydrochloric acid is added to the dezincification solution to adjust the pH value of the corrosion-inhibiting dezincification solution to less than or equal to 1;

[0068] When the zinc ion online detection system detects that the zinc ion content in the corrosion-inhibiting dezincification liquid is 190 g / L, the corrosion-inhibiting dezincification liquid is pumped into the treatment tank in step 7, and the standby dezincification tank starts working at this time;

[0069] Step 5, immersing the dezincified steel guardrail plate in step 4 into a third rinsing tank at room temperature for rinsing once, and then immersing it into a fourth rinsing tank for rinsing once;

[0070] Step 6, cutting, truncating, packing, and briquetting the steel guardrail panels rinsed in step 5, and storing them for sale;

[0071] Step 7, adjusting the pH value of the dezincification liquid pumped in step 4 to 4 with industrial hydrochloric acid, adding hydrogen peroxide to the dezincification liquid and assisting stirring, then standing and settling, filtering and pouring the trough, adding zinc powder in an amount of 50g / cubic meter to the dezincification liquid in the trough and assisting stirring, then standing and settling, filtering and pouring the trough, and adding industrial hydrochloric acid to the dezincification liquid in the trough to adjust the pH value to 4;

[0072] Step 8, the dezincification liquid treated in step 7 is pumped into an evaporator, kept at 265° C. for 6 hours, and cooled to obtain zinc chloride crystal particles; a certain amount of zinc chloride crystals are taken and completely dissolved with analytical pure dilute hydrochloric acid, and the content of zinc chloride in the zinc chloride crystals is 95.79% and the content of iron in the zinc chloride crystals is 0.05%.

[0073] Cut 1 kg of the steel guardrail plate from step 6 and completely dissolve it with analytical pure hydrochloric acid. ICP-AES detection and calculation show that the zinc content in the steel guardrail plate is 8.1×10 -7 g, indicating that the two waves of steel guardrail plates in step 6 contain almost no zinc.

[0074] Embodiment 3:

[0075] Categories of galvanized steel scrap to be recycled: waste galvanized isolation fences for urban roads with polyurethane topcoat on the surface, material Q195, average thickness of the galvanized layer 106μm, and topcoat shedding rate of about 6% (area ratio).

[0076] Step 1, sorting the waste galvanized isolation fence, removing the remaining bolts, hooks and other connectors or fasteners, and removing the remaining waste plastics, tree leaves, etc.;

[0077] Step 2, immersing 3 tons of the isolation fences sorted in step 1 in a first pretreatment tank at room temperature, wherein the pretreatment liquid in the first pretreatment tank is a commonly used paint stripping cleaning agent dilution liquid, and ultrasonic-assisted cleaning is performed for 5 minutes;

[0078] Step 3, immersing the isolation fence treated in step 2 in a second rinsing tank at room temperature;

[0079] Step 4, immersing the isolation fence treated in step 3 in a corrosion-inhibiting dezincification solution prepared by hydrochloric acid, wherein the initial pH value of the corrosion-inhibiting dezincification solution is not greater than 1, and a hexamethylenetetramine corrosion inhibitor with a mass fraction of 1.0% is added to the dezincification solution, and the dezincification time is extended by 3 minutes until bubbles visible to the naked eye just disappear on the surface of the isolation fence;

[0080] The isolation fence is used as a batch of 3 tons, and multiple batches are cyclically processed in steps 1 to 4. When the pH value of the corrosion-inhibiting dezincification solution is greater than 5, industrial hydrochloric acid is added to the dezincification solution to adjust the pH value of the corrosion-inhibiting dezincification solution to less than or equal to 1;

[0081] When the zinc ion online detection system detects that the zinc ion content in the corrosion-inhibiting dezincification liquid is 195 g / L, the corrosion-inhibiting dezincification liquid is pumped into the treatment tank in step 7, and the standby dezincification tank starts working at this time;

[0082] Step 5, immersing the isolation fence after dezincification in step 4 into a third rinsing tank at room temperature for rinsing once, and then immersing it into a fourth rinsing tank for rinsing once;

[0083] Step 6, cutting, truncating, packing, and briquetting the isolation fences rinsed in step 5, and storing them for sale;

[0084] Step 7, adjusting the pH value of the dezincification liquid pumped in step 4 to 3.7 with industrial hydrochloric acid, adding hydrogen peroxide to the dezincification liquid and assisting stirring, then standing and settling, filtering and pouring the trough, adding zinc powder in an amount of 50g / cubic meter to the dezincification liquid in the trough and assisting stirring, then standing and settling, filtering and pouring the trough, and adding industrial hydrochloric acid to the dezincification liquid in the trough to adjust the pH value to 3.7;

[0085] Step 8, the dezincification liquid treated in step 7 is pumped into an evaporator, kept at 300° C. for 5 hours, and cooled to obtain zinc chloride crystal particles; a certain amount of zinc chloride crystals are taken and completely dissolved with analytical pure dilute hydrochloric acid, and ICP-AES is used for detection and calculation. The zinc chloride content in the zinc chloride crystals is 96.72%, and the iron content in the zinc chloride crystals is 0.009%.

[0086] Take 1 kg of the isolation fence from step 6 and completely dissolve it with analytical pure hydrochloric acid. ICP-AES detection and calculation show that the zinc content in the isolation fence is 9.5×10 -6 g, indicating that the isolation fence in step 6 contains almost no zinc.

[0087] Embodiment 4:

[0088] Categories of galvanized scrap steel to be recycled: disc-type scaffolding uprights, material Q355, average thickness of the galvanized layer 76μm.

[0089] Step 1: manually sort the scaffolding poles, remove the mixed concrete slag, remove the concrete adhesion layer remaining on the surface of individual scaffolding poles, and pick up individual scaffolding small components;

[0090] Step 2, immersing 5 tons of scaffolding poles sorted in step 1 into a first pretreatment tank at room temperature, wherein the pretreatment solution in the first pretreatment tank is a weak alkaline solution with a pH value of 10, and performing ultrasonic-assisted cleaning for 8 minutes;

[0091] Step 3, immersing and rinsing the scaffolding poles treated in step 2 in a second rinsing tank at room temperature;

[0092] Step 4, immersing the scaffolding pole treated in step 3 into a corrosion-inhibiting dezincification solution prepared by hydrochloric acid, wherein the initial pH value of the corrosion-inhibiting dezincification solution is not greater than 1, and a hexamethylenetetramine corrosion inhibitor with a mass fraction of 1.2% is added to the dezincification solution, and the dezincification time is extended by 5 minutes until bubbles visible to naked eyes just disappear on the surface of the scaffolding pole;

[0093] The scaffolding poles are processed in steps 1 to 4 in a cycle with 5 tons as one batch. When the pH value of the corrosion-inhibiting dezincification solution is greater than 5, industrial hydrochloric acid is added to the dezincification solution to adjust the pH value of the corrosion-inhibiting dezincification solution to less than or equal to 1.

[0094] When the zinc ion online detection system detects that the zinc ion content in the corrosion-inhibiting dezincification liquid is 200 g / L, the corrosion-inhibiting dezincification liquid is pumped into the treatment tank in step 7, and the standby dezincification tank starts working at this time;

[0095] Step 5, immersing the scaffolding pole after dezincification in step 4 into a third rinsing tank at room temperature for rinsing once, and then immersing it into a fourth rinsing tank for rinsing once;

[0096] Step 6, packing and briquetting the scaffolding poles rinsed in step 5, and storing them for sale;

[0097] Step 7, adjusting the pH value of the dezincification liquid pumped in step 4 to 4 with industrial hydrochloric acid, adding hydrogen peroxide to the dezincification liquid and assisting stirring, then standing and settling, filtering and pouring the trough, adding zinc powder in an amount of 60g / cubic meter to the dezincification liquid in the trough and assisting stirring, then standing and settling, filtering and pouring the trough, and adding industrial hydrochloric acid to the dezincification liquid in the trough to adjust the pH value to 4;

[0098] Step 8, the dezincification solution treated in step 7 is pumped into an evaporator, kept at 280°C for 4.5 hours, and collected after cooling to obtain a concentrated zinc chloride solution; ICP-AES detection and calculation show that the zinc chloride content in the concentrated zinc chloride solution is 50.08%, and the Fe content in the concentrated zinc chloride solution is 2.34%. 2+ The content is 0.0075g / L.

[0099] Take one scaffolding pole from step 6, cut off any section and weigh it, dissolve it completely with analytical pure hydrochloric acid, and detect and calculate it by ICP-AES. The zinc content in the scaffolding pole is 5.4×10 -8 g, indicating that the scaffolding uprights in step 6 contain almost no zinc.

[0100] Embodiment 5:

[0101] Categories of galvanized scrap steel to be recycled: disc-type scaffolding uprights, material Q355, average thickness of the galvanized layer 76μm.

[0102] Step 1: manually sort the scaffolding poles, remove the mixed concrete slag, remove the concrete adhesion layer remaining on the surface of individual scaffolding poles, and pick up individual scaffolding small components;

[0103] Step 2, immersing 5 tons of scaffolding poles sorted in step 1 into a first pretreatment tank at room temperature, wherein the pretreatment solution in the first pretreatment tank is a weak alkaline solution with a pH value of 10, and performing ultrasonic-assisted cleaning for 8 minutes;

[0104] Step 3, immersing and rinsing the scaffolding poles treated in step 2 in a second rinsing tank at room temperature;

[0105] Step 4, immersing the scaffolding pole treated in step 3 into a corrosion-inhibiting dezincification solution prepared by hydrochloric acid, wherein the initial pH value of the corrosion-inhibiting dezincification solution is not greater than 1, and a hexamethylenetetramine corrosion inhibitor with a mass fraction of 1.2% is added to the dezincification solution, and the dezincification time is extended by 5 minutes until bubbles visible to naked eyes just disappear on the surface of the scaffolding pole;

[0106] The scaffolding poles are processed in steps 1 to 4 in a cycle with 5 tons as one batch. When the pH value of the corrosion-inhibiting dezincification solution is greater than 5, industrial hydrochloric acid is added to the dezincification solution to adjust the pH value of the corrosion-inhibiting dezincification solution to less than or equal to 1.

[0107] When the zinc ion online detection system detects that the zinc ion content in the corrosion-inhibiting dezincification liquid is 210 g / L, the corrosion-inhibiting dezincification liquid is pumped into the treatment tank in step 7, and the standby dezincification tank starts working at this time;

[0108] Step 5, immersing the scaffolding pole after dezincification in step 4 into a third rinsing tank at room temperature for rinsing once, and then immersing it into a fourth rinsing tank for rinsing once;

[0109] Step 6, packing and briquetting the scaffolding poles rinsed in step 5, and storing them for sale;

[0110] Step 7, adjusting the pH value of the dezincification liquid pumped in step 4 to 4 with industrial hydrochloric acid, adding hydrogen peroxide to the dezincification liquid and assisting stirring, then standing and settling, filtering and pouring the trough, adding zinc powder in an amount of 60g / cubic meter to the dezincification liquid in the trough and assisting stirring, then standing and settling, filtering and pouring the trough, and adding industrial hydrochloric acid to the dezincification liquid in the trough to adjust the pH value to 4;

[0111] Step 8, the dezincification solution treated in step 7 is pumped into an evaporator, kept at 280°C for 4.5 hours, and collected after cooling to obtain a concentrated zinc chloride solution; ICP-AES detection and calculation show that the zinc chloride content in the concentrated zinc chloride solution is 50.87%, and the Fe content in the concentrated zinc chloride solution is 2.37%. 2+ The content is 0.0099g / L.

[0112] Take one scaffolding pole from step 6, cut off any section and weigh it, dissolve it completely with analytical pure hydrochloric acid, and detect and calculate it by ICP-AES. The zinc content in the scaffolding pole is 1.1×10 -8 g, indicating that the scaffolding uprights in step 6 contain almost no zinc.

[0113] It was found in the operation process of Example 4 and Example 5 that after the online detection value of zinc ions in the corrosion inhibition dezincification tank reached 195g / L, the scaffolding poles continued to be placed into the tank, the dezincification treatment speed of step 4 was significantly reduced, and the number and speed of bubbles appearing above the dezincification tank were also significantly slowed down, which also explained the priority and rationality of the zinc content threshold of 185g / L in the dezincification tank and the zinc ion content of 185g / L-195g / L in the dezincification solution being suitable for subsequent treatment.

[0114] The embodiments of the present application have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technology in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A method for recovering zinc chloride from galvanized steel scrap, characterized in that: The following steps are involved: Step 1, sorting and processing, according to whether the galvanized scrap steel has a paint coating on its surface, to divide it into bare galvanized scrap steel and galvanized scrap steel with a paint film on its surface; Step 2, pre-treatment, cleaning the surface of the galvanized steel scrap according to the two surface states of the sorted galvanized steel scrap, removing surface grease, paint film residues and dirt; Step 3, performing a first rinsing treatment, immersing the pretreated galvanized scrap steel in rinsing water for a first rinsing; Step 4, performing corrosion inhibition and dezincification treatment, immersing the galvanized scrap steel after rinsing treatment into a dezincification solution in a dezincification tank, wherein the dezincification solution is a pickling solution with a corrosion inhibitor added thereto, removing the zinc coating on the surface of the galvanized scrap steel through a solution reaction, and detecting the content of zinc ions in the dezincification tank in real time online; Step 5, performing a second rinsing treatment, rinsing the scrap steel substrate after corrosion inhibition and dezincification with rinsing water for a second time to remove the residual zinc ions on the surface of the steel substrate; Step 6, cutting the scrap steel substrate after the second rinse into a suitable size or structure for easy subsequent packaging or briquetting; Step 7, performing a composite impurity removal treatment, when the zinc ion content in the dezincification tank is within a set zinc content threshold range, performing continuous treatments of oxidation precipitation, first filtration, zinc powder reduction and second filtration on the dezincification liquid in the dezincification tank, and performing online detection of the zinc ion content; Step 8, performing evaporation treatment, heating and evaporating the dezincification liquid after the composite impurity removal treatment at a set temperature in an evaporator to obtain a zinc chloride aqueous solution or zinc chloride crystals.

2. The method for recovering zinc chloride from galvanized steel scrap according to claim 1, characterized in that: In step 2, when performing surface cleaning, if the galvanized scrap steel is a paint film galvanized scrap steel with a paint coating on the surface, a paint stripping cleaning method is adopted; if the galvanized scrap steel is a bare galvanized scrap steel without a paint coating on the surface, an alkali washing method is adopted.

3. The method for recovering zinc chloride from galvanized steel scrap according to claim 2, characterized in that: The alkaline cleaning method is to use a weak alkaline cleaning solution and assist with ultrasonic cleaning; the paint stripping cleaning method is to use a neutral solvent-type paint stripping cleaning solution and assist with ultrasonic cleaning.

4. The method for recovering zinc chloride from galvanized steel scrap according to claim 1, characterized in that: In step 4, the mass percentage of the corrosion inhibitor added to the pickling solution is 0.8-1.5%.

5. The method for recovering zinc chloride from galvanized steel scrap according to claim 1, characterized in that: In step 5, during the second rinsing, the scrap steel substrate is rinsed 1 to 2 times with rinsing water.

6. The method for recovering zinc chloride from galvanized steel scrap according to claim 1, characterized in that: In step 7, the zinc content threshold range is 185 g / L to 195 g / L.

7. The method for recovering zinc chloride from galvanized steel scrap according to claim 1, characterized in that: In step 7, when the oxidation precipitation treatment is performed, hydrogen peroxide is used for oxidation treatment. During the oxidation treatment, the pH value of the dezincification solution is maintained between 3.5 and 4, and the pH value is maintained by adjusting hydrogen peroxide or hydrochloric acid.

8. The method for recovering zinc chloride from galvanized steel scrap according to claim 1, characterized in that: In step 7, when the zinc powder reduction treatment is performed, the amount of zinc powder added is 50 g to 100 g per cubic meter of the dezincification liquid.

9. The method for recovering zinc chloride from galvanized steel scrap according to claim 1, characterized in that: In step 8, the zinc chloride aqueous solution has a zinc chloride content of not less than 50% by mass and Fe 2+ The mass content is not higher than 0.02g / L~0.5g / L.

10. The method for recovering zinc chloride from galvanized steel scrap according to claim 1, characterized in that: In step 8, the mass content of zinc chloride in the zinc chloride crystals is not less than 95%.

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