阅读说明：本技术 不锈钢酸洗废水处理过程中产生的硝酸钙的处理方法 (Method for treating calcium nitrate generated in stainless steel pickling wastewater treatment process ) 是由 方劲松 叶众欢 张冶 杨鸿辉 于 2021-10-16 设计创作，主要内容包括：本发明公开了一种不锈钢酸洗废水处理过程中产生的硝酸钙的处理方法,包括以下步骤：S1、将硝酸钙废水过滤后送入MED降膜蒸发器,其浓缩倍数控制在10-20倍；S2、将预浓缩液加入MVR强制循环蒸发结晶器进一步浓缩,其浓缩倍数控制在2-5倍；S3、将步骤S2中得到的硝酸钙浓缩液与硫酸在1号、2号、3号反应罐进行分步依次反应；S4、将3号反应罐的产物进行固液分离,将滤液泵入硝酸储罐进行存储；S5、对1号、2号、3号反应罐压滤后所得的滤饼进行在线洗涤处理后可作为建筑石膏进行资源化回收再利用。本发明具有以下优点和效果：能对硝酸钙进行有效处理,实现资源化利用,从而为企业处理污染物的同时也能给企业创造经济价值。(The invention discloses a method for treating calcium nitrate generated in a stainless steel pickling wastewater treatment process, which comprises the following steps: s1, filtering the calcium nitrate wastewater, and feeding the calcium nitrate wastewater into an MED falling film evaporator, wherein the concentration multiple is controlled to be 10-20 times; s2, adding the pre-concentrated solution into an MVR forced circulation evaporation crystallizer for further concentration, wherein the concentration multiple is controlled to be 2-5 times; s3, carrying out step-by-step sequential reaction on the calcium nitrate concentrated solution obtained in the step S2 and sulfuric acid in reaction tanks No. 1, No. 2 and No. 3; s4, performing solid-liquid separation on the product of the reaction tank No. 3, and pumping the filtrate into a nitric acid storage tank for storage; s5, carrying out on-line washing treatment on filter cakes obtained after filter pressing of the reaction tanks No. 1, No. 2 and No. 3, and then recycling the filter cakes as building gypsum. The invention has the following advantages and effects: can effectively treat the calcium nitrate and realize resource utilization, thereby creating economic value for enterprises while treating pollutants.)

1. A method for treating calcium nitrate generated in the stainless steel pickling wastewater treatment process is characterized by comprising the following steps:

s1, filtering the calcium nitrate wastewater, feeding the calcium nitrate wastewater into an MED falling film evaporator, and carrying out evaporation concentration on the calcium nitrate wastewater to obtain a pre-concentrated solution, wherein the concentration multiple is controlled to be 10-20 times;

s2, adding the pre-concentrated solution into an MVR forced circulation evaporation crystallizer for further concentration, wherein the main component of the obtained concentrated solution is calcium nitrate, the concentration multiple of the calcium nitrate is controlled to be 2-5 times, and the mass concentration of the obtained calcium nitrate is 30-55%;

s3, carrying out step-by-step reaction on the calcium nitrate concentrated solution obtained in the step S2 and sulfuric acid, wherein the step-by-step reaction can be divided into 1) -4):

1) adding a certain amount of calcium nitrate concentrated solution into a No. 1 reaction tank, pumping a certain amount of sulfuric acid, reacting for a period of time, and performing solid-liquid separation;

2) adding the filtrate in the reaction tank No. 1 into the reaction tank No. 2, pumping a certain amount of sulfuric acid, and carrying out solid-liquid separation after reacting for a period of time;

3) adding the filtrate in the reaction tank No. 2 into the reaction tank No. 3, pumping a certain amount of sulfuric acid, and carrying out solid-liquid separation after reacting for a period of time;

4) meanwhile, continuously adding the calcium nitrate concentrated solution into the reaction tank No. 1, pumping a certain amount of sulfuric acid, and circulating the steps 1) -3);

s4, performing solid-liquid separation on the product of the reaction tank No. 3, and pumping the filtrate into a nitric acid storage tank for storage;

s5, carrying out on-line washing treatment on filter cakes obtained after filter pressing of the reaction tanks No. 1, No. 2 and No. 3, and then recycling the filter cakes as building gypsum.

2. The method for treating calcium nitrate generated in the process of treating stainless steel pickling wastewater according to claim 1, wherein the method comprises the following steps: in the steps 1) -3), the adding amount of the sulfuric acid with the concentration of 98 percent is 10-100 percent of the molar amount of the calcium nitrate, and the reaction time is 10-120 min.

3. The method for treating calcium nitrate generated in the process of treating stainless steel pickling wastewater according to claim 1, wherein the method comprises the following steps: the filter cake treatment step in step S5 includes, but is not limited to, filtration, primary pressing, washing, secondary filter pressing, air drying, etc., to reduce the filter cake moisture content to an optimum level.

4. The method for treating calcium nitrate generated in the process of treating stainless steel pickling wastewater according to claim 1, wherein the method comprises the following steps: the condensed water produced by the evaporation and concentration in steps S1 and S2 is recycled.

5. The method for treating calcium nitrate generated in the process of treating stainless steel pickling wastewater according to claim 1, wherein the method comprises the following steps: the nitric acid produced by the reaction of calcium nitrate with sulfuric acid in step S3 can be recycled to the stainless steel pickling stage.

Technical Field

The invention relates to the technical field of stainless steel pickling wastewater treatment, in particular to a method for treating calcium nitrate generated in the stainless steel pickling wastewater treatment process.

Background

Because the stainless steel pickling wastewater contains a large amount of heavy metals such as nickel, iron and the like, the prior art effectively precipitates the heavy metals such as iron, nickel, chromium and the like by adding lime to adjust the pH value, thereby realizing the standard discharge of the heavy metals.

However, high-concentration calcium nitrate is generated in the wastewater neutralized by adding lime, and the calcium nitrate cannot be directly discharged and is difficult to treat. Can concentrate the back with calcium nitrate and concentrate again and handle, but the calcium nitrate concentrate is easy explosion hazard waste, handles according to danger waste and not only can further cause the increase of water treatment cost, also can make the resource wherein not utilized and cause huge waste. The present invention was made in light of the above problems.

Disclosure of Invention

The invention aims to provide a method for treating calcium nitrate generated in the stainless steel pickling wastewater treatment process, which can effectively treat the calcium nitrate generated in the stainless steel pickling wastewater treatment process, realize resource utilization, and further create economic value for enterprises while treating pollutants.

The technical purpose of the invention is realized by the following technical scheme: a method for treating calcium nitrate generated in the stainless steel pickling wastewater treatment process comprises the following steps:

s1, filtering the calcium nitrate wastewater, feeding the calcium nitrate wastewater into an MED falling film evaporator, and carrying out evaporation concentration on the calcium nitrate wastewater to obtain a pre-concentrated solution, wherein the concentration multiple is controlled to be 10-20 times;

s2, adding the pre-concentrated solution into an MVR forced circulation evaporation crystallizer for further concentration, wherein the main component of the obtained concentrated solution is calcium nitrate, the concentration multiple of the calcium nitrate is controlled to be 2-5 times, and the mass concentration of the obtained calcium nitrate is 30-55%;

s3, carrying out step-by-step reaction on the calcium nitrate concentrated solution obtained in the step S2 and sulfuric acid, wherein the step-by-step reaction can be divided into 1) -4):

1) adding a certain amount of calcium nitrate concentrated solution into a No. 1 reaction tank, pumping a certain amount of sulfuric acid, reacting for a period of time, and performing solid-liquid separation;

2) adding the filtrate in the reaction tank No. 1 into the reaction tank No. 2, pumping a certain amount of sulfuric acid, and carrying out solid-liquid separation after reacting for a period of time;

3) adding the filtrate in the reaction tank No. 2 into the reaction tank No. 3, pumping a certain amount of sulfuric acid, and carrying out solid-liquid separation after reacting for a period of time;

4) meanwhile, continuously adding the calcium nitrate concentrated solution into the reaction tank No. 1, pumping a certain amount of sulfuric acid, and circulating the steps 1) -3);

s4, performing solid-liquid separation on the product of the reaction tank No. 3, and pumping the filtrate into a nitric acid storage tank for storage;

s5, carrying out on-line washing treatment on filter cakes obtained after filter pressing of the reaction tanks No. 1, No. 2 and No. 3, and then recycling the filter cakes as building gypsum.

By adopting the technical scheme, the step does not relate to the removal process of heavy metals in the stainless steel wastewater at the front end, the stainless steel pickling wastewater after lime neutralization is treated, the MED falling-film evaporator is industrial equipment, the MVR forced circulation evaporation crystallizer is industrial equipment, and the evaporation and concentration process of calcium nitrate effluent is carried out by combining with the MED falling-film evaporator. The reaction tanks No. 1, No. 2 and No. 3 are large reaction vessels, have a stirring function and are used for the reaction of calcium nitrate and sulfuric acid.

Further setting the following steps: in the steps 1) -3), the adding amount of the sulfuric acid with the concentration of 98 percent is 10-100 percent of the molar amount of the calcium nitrate, and the reaction time is 10-120 min.

By adopting the technical scheme, the reaction tanks No. 1, No. 2 and No. 3 are provided with heat exchange devices, the heat released by the reaction is led out, and the reaction temperature is kept within the range of 20-40 ℃.

Further setting the following steps: the filter cake treatment step in step S5 includes, but is not limited to, filtration, primary pressing, washing, secondary filter pressing, air drying, etc., to reduce the filter cake moisture content to an optimum level.

Further setting the following steps: the quality of the condensed water generated by evaporation and concentration in the steps S1 and S2 can meet the requirement of production water for recycling and can also reach the standard for discharge.

Further setting the following steps: the nitric acid produced by the reaction of calcium nitrate with sulfuric acid in step S3 can be recycled to the stainless steel pickling stage.

In conclusion, the invention has the following beneficial effects: the method can effectively realize the resource utilization of the calcium nitrate hazardous waste in the wastewater, firstly realizes the reuse of part of the reclaimed water through the evaporation concentration process, then the concentrated calcium nitrate reacts with the cheap sulfuric acid to generate the nitric acid and the calcium sulfate, wherein the nitric acid can be reused to save the cost, the calcium sulfate can be sold as a gypsum raw material, finally realizes the on-site disposal and the resource utilization of the high-concentration calcium nitrate wastewater, and can create economic value while treating pollutants for enterprises.

Drawings

FIG. 1 is a process flow diagram of the present invention.

In the figure: 1. an MED falling film evaporator; 2. MVR forced circulation evaporation crystallizer; 3. a reaction tank No. 1; 4. a reaction tank No. 2; 5. and a reaction tank No. 3.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings.

Example one

Referring to fig. 1, a method for treating calcium nitrate generated in a stainless steel pickling wastewater treatment process includes filtering pretreated wastewater containing calcium nitrate, feeding the filtered wastewater into an MED falling film evaporator 1 to obtain 20% concentrated solution, pumping the 20% concentrated solution into an MVR forced circulation evaporation crystallizer 2, feeding 80% condensed water generated by reaction into a clean water tank, and concentrating the concentrated solution by 10 times through MED + MVR to obtain final concentrated solution. The final concentrate was added to tank 3, No. 1, for 10 t, while 33.3% of the stoichiometric sulfuric acid (98%) was pumped in, and reacted for 10 min. Pumping the solid-containing material liquid in the reaction tank No. 1 and No. 3 into a solid-liquid separator for solid-liquid separation, pumping the separated filtrate into the reaction tank No. 2 and simultaneously inputting 33.3 percent of stoichiometric sulfuric acid for reaction for 10 min. And pumping the solid-containing material liquid in the reaction tank No. 2 4 into a solid-liquid separator for solid-liquid separation, and pumping the separated separation liquid into the reaction tank No. 3 5 and simultaneously pumping 33.3% of the stoichiometric sulfuric acid. Simultaneously to the reaction tank No. 13, 10 t of the final concentrate was added while pumping 33.3% of the stoichiometric sulfuric acid, and the above steps were repeated. And pumping the solid-containing material liquid in the No. 3 reaction tank 5 into a solid-liquid separator for filter pressing, and pumping the generated filtrate into a nitric acid storage tank. Through the steps, the calcium nitrate can be gradually converted into nitric acid and gypsum (CaSO)₄•2H₂O), realizing the resource utilization of the calcium nitrate.

Example two

A method for treating calcium nitrate generated in the process of treating stainless steel pickling wastewater comprises the steps of filtering pretreated wastewater containing calcium nitrate, then feeding the filtered wastewater into an MED falling film evaporator 1 to obtain 15% concentrated solution, pumping the 15% concentrated solution into an MVR forced circulation evaporation crystallizer 2, feeding 90% condensed water generated by reaction into a clean water tank, and concentrating the concentrated solution by 25 times through MED and MVR to obtain the final concentrated solution. The final concentrate was added to tank 3, No. 1, for 10 t, while 33.3% of the stoichiometric amount of sulfuric acid (98%) was pumped and reacted for 60 min. Pumping the solid-containing material liquid in the reaction tank No. 1 and No. 3 into a solid-liquid separator for solid-liquid separation, pumping the separated filtrate into the reaction tank No. 2 and simultaneously inputting 33.3 percent of stoichiometric sulfuric acid for reaction for 60 min. And pumping the solid-containing material liquid in the reaction tank No. 2 4 into a solid-liquid separator for solid-liquid separation, and pumping the separated separation liquid into the reaction tank No. 3 5 and simultaneously pumping 33.3% of the stoichiometric sulfuric acid. At the same time, 10 t of the final concentrate was added to tank 3, while 33.3% of the stoichiometric amount of sulfuric acid was pumped, and the above steps were cycled. And pumping the solid-containing material liquid in the No. 3 reaction tank 5 into a solid-liquid separator for filter pressing, and pumping the generated filtrate into a nitric acid storage tank. Through the steps, the calcium nitrate can be gradually converted into the nitric acid and the calcium sulfate, and the resource utilization of the calcium nitrate is realized.

EXAMPLE III

A method for treating calcium nitrate generated in the process of treating stainless steel pickling wastewater comprises the steps of filtering pretreated wastewater containing calcium nitrate, enabling the filtered wastewater to enter an MED falling film evaporator 1 to obtain 10% concentrated solution, pumping the 10% concentrated solution into an MVR forced circulation evaporation crystallizer 2, enabling 85% condensed water generated by reaction to enter a clean water tank, and concentrating the concentrated solution by 40 times through MED and MVR to obtain final concentrated solution. Concentrating the final productThe solution is added into a reaction tank 3 No. 1 for 10 t, and simultaneously 25 percent of stoichiometric sulfuric acid (98 percent) is pumped for reaction for 120 min. Pumping the solid-containing material liquid in the reaction tank No. 1 and No. 3 into a solid-liquid separator for solid-liquid separation, pumping the separated filtrate into the reaction tank No. 2 and simultaneously inputting 30 percent of stoichiometric sulfuric acid for reaction for 120 min. And pumping the solid-containing material liquid in the reaction tank No. 2 4 into a solid-liquid separator for solid-liquid separation, and pumping the separated separation liquid into the reaction tank No. 3 5 and simultaneously pumping 45% of the stoichiometric sulfuric acid. At the same time, 10 t of the final concentrate was added to tank 3, while 25% of the stoichiometric amount of sulfuric acid was pumped in, and the above steps were cycled. And pumping the solid-containing material liquid in the No. 3 reaction tank 5 into a solid-liquid separator for filter pressing, and pumping the generated filtrate into a nitric acid storage tank. Through the steps, the calcium nitrate can be gradually converted into nitric acid and gypsum (CaSO)₄•2H₂O), realizing the resource utilization of the calcium nitrate.

The invention discloses a physical and chemical treatment method, and particularly relates to a method for recycling calcium nitrate generated in the stainless steel pickling wastewater treatment process. According to the invention, calcium nitrate wastewater is evaporated and concentrated through MED and MVR evaporators, then the concentrated solution reacts with concentrated sulfuric acid in a reaction tank to convert the concentrated solution into nitric acid and calcium sulfate precipitate, and solid-liquid separation is carried out through pressure filtration, so that the resource conversion of calcium nitrate in wastewater can be realized. The whole process does not need complex equipment, is simple to operate, and can effectively realize the resource treatment of the calcium nitrate wastewater. Gypsum (CaSO) prepared by treatment process₄•2H₂O), the content of the compound meets the content requirement of national standard (GB/T37785-2019) of flue gas desulfurization gypsum, the leaching toxicity is completely lower than the limit value of the hazardous waste identification standard specified in hazardous waste identification standard toxic substance content identification (GB 5085.6-2007), and the compound can be recycled.

The method can generate the byproduct calcium sulfate while reducing the wastewater treatment cost, can prepare gypsum for sale after simple treatment, realizes comprehensive resource recycling, and can reuse the generated nitric acid for pickling of stainless steel, thereby further reducing the cost in the production stage. The method can be widely applied to the recycling treatment of calcium nitrate in production wastewater in enterprises.

The present embodiment is only for explaining the present invention, and it is not limited to the present invention, and those skilled in the art can make modifications of the present embodiment without inventive contribution as needed after reading the present specification, but all of them are protected by patent law within the scope of the claims of the present invention.