阅读说明：本技术 一种从污泥焚烧底灰中回收钙磷肥的方法 (Method for recovering calcium phosphate fertilizer from sludge incineration bottom ash ) 是由 陈滢 刘敏 徐灵芳 于 2020-05-20 设计创作，主要内容包括：本发明公开了一种从污泥焚烧底灰中回收钙磷肥的方法。该方法包括以下步骤：(1)将污泥焚烧底灰干燥至恒重,冷却备用；(2)将盐酸溶液与污泥焚烧底灰混合,搅拌5～60min后,过滤,得富磷提取液；(3)将氢氧化钙加入至富磷提取液中,反应1～60min后,于100～120℃对反应液进行蒸发浓缩,使溶液表面形成晶膜；(4)于室温自然冷却结晶,过滤,收集上部晶体,晶体风干后即得磷肥。本申请采用低液固比的方式进行提取,不会产生大量废液,并且低液固比能在磷提取的同时达到富集的效果,能够降低后续处理成本,同时,采用盐酸进行处理还不会产生新的固体物质阻碍提取反应的进行,具有较高的提取率,提取得到的磷肥纯度高。(The invention discloses a method for recovering a calcium phosphate fertilizer from sludge incineration bottom ash. The method comprises the following steps: (1) drying the sludge incineration bottom ash to constant weight, and cooling for later use; (2) mixing the hydrochloric acid solution with the sludge incineration bottom ash, stirring for 5-60 min, and filtering to obtain a phosphorus-rich extracting solution; (3) adding calcium hydroxide into the phosphorus-rich extracting solution, reacting for 1-60 min, and then evaporating and concentrating the reaction solution at 100-120 ℃ to form a crystal film on the surface of the solution; (4) naturally cooling and crystallizing at room temperature, filtering, collecting upper crystals, and air-drying the crystals to obtain the phosphate fertilizer. This application adopts the mode of low liquid-solid ratio to extract, can not produce a large amount of waste liquids to low liquid-solid ratio can reach the effect of enrichment in the phosphorus extraction, can reduce the subsequent processing cost, and simultaneously, adopts hydrochloric acid to handle and still can not produce new solid matter and hinder the going on of extraction reaction, has higher extraction rate, and the phosphorus fertilizer purity that obtains of drawing is high.)

1. A method for recovering a calcium phosphate fertilizer from sludge incineration bottom ash is characterized by comprising the following steps:

(1) drying the sludge incineration bottom ash to constant weight, and cooling to room temperature for later use;

(2) heating a hydrochloric acid solution with the concentration of 1.5-3.0 mol/L to 25-45 ℃, then mixing the hydrochloric acid solution with sludge incineration bottom ash in a liquid-solid ratio of less than or equal to 5mL/g, stirring at 50-400 rpm for 5-60 min, and filtering to obtain a phosphorus-rich extracting solution;

(3) adding calcium hydroxide into the phosphorus-rich extracting solution, reacting for 1-60 min, and then carrying out evaporation concentration on the reaction solution at 100-120 ℃ for 30-100 min to form a crystal film on the surface of the solution; the molar ratio of the calcium hydroxide to the phosphoric acid in the phosphorus-rich extracting solution is 0.5: 1-6: 1;

(4) and (4) naturally cooling and crystallizing the solution obtained in the step (3) at room temperature, filtering, collecting crystals on the upper part, and air-drying the crystals to obtain the phosphate fertilizer.

2. The method for recovering the calcium phosphate fertilizer from the sludge incineration bottom ash according to claim 1, wherein the liquid-solid ratio of the hydrochloric acid solution to the sludge incineration bottom ash is 2-5 mL/g.

3. The method for recovering a calcium phosphate fertilizer from sludge incineration bottom ash according to claim 2, characterized in that the liquid-solid ratio of the hydrochloric acid solution to the sludge incineration bottom ash is 3 mL/g.

4. The method for recovering a calcium phosphate fertilizer from sludge incineration bottom ash according to claim 1 or 2, characterized in that the concentration of the hydrochloric acid solution is 2.0 mol/L.

5. The method for recovering a calcium phosphate fertilizer from sludge incineration bottom ash according to claim 1, wherein the process of stirring and mixing the hydrochloric acid solution and the sludge incineration bottom ash is as follows: stirring at 200rpm for 10min at room temperature.

6. The method for recovering a calcium phosphate fertilizer from sludge incineration bottom ash according to claim 1, characterized in that the molar ratio of the calcium hydroxide to the phosphoric acid in the phosphorus-rich extracting solution is 2: 1.

7. The method for recovering a calcium phosphate fertilizer from sludge incineration bottom ash as recited in claim 1, characterized in that the reaction time of the calcium hydroxide and the phosphorus-rich extracting solution is 30 min.

8. The method for recovering a calcium phosphate fertilizer from sludge incineration bottom ash according to claim 1, characterized in that the temperature of evaporation concentration is 105 ℃ and the time is 60 min.

9. The method for recovering a calcium phosphate fertilizer from sludge incineration bottom ash according to claim 1, characterized in that the sludge incineration bottom ash is sludge incineration bottom ash remained after residual sludge incineration in a sewage plant.

Technical Field

The invention belongs to the technical field of resource recovery of sewage treatment plants, and particularly relates to a method for recovering a calcium phosphate fertilizer from sludge incineration bottom ash.

Background

With the reduction of the storage amount of the phosphorite, the reduction of the quality and the increase of the price of the phosphorite, the research on new production substitutes of the agricultural phosphate fertilizers is promoted. The sludge incineration bottom ash is ash obtained by incinerating residual sludge in the urban sewage plant, and has great recycling potential due to the rich phosphorus. The sludge incineration bottom ash can be treated by a wet chemical method, namely a chemical agent, and phosphorus can be extracted from the sludge incineration bottom ash. This not only can alleviate the pressure of disposing of the bottom ash, but also can recover phosphorus resources.

At present, the phosphorus in the bottom ash of sludge incineration is extracted by sulfuric acid, but in the process, the sulfuric acid and calcium-containing compounds in the slag can generate gypsum (CaSO)₄). Gypsum is slightly soluble in water, which can hinder the subsequent extraction process, i.e., the reaction rate is reduced, and meanwhile, the subsequent utilization of bottom ash is not facilitated. In addition, in terms of condition control, the extraction of phosphorus is mainly carried out at a high liquid-solid ratio (ratio of the volume of the medicament to the mass of the sludge incineration bottom ash), such as 20mL/g to 150 mL/g. Although higher phosphorus extraction rate can be obtained by high liquid-solid ratio, the phosphorus content in the unit volume of the extracting solution is low, so that more cost is needed for the subsequent phosphorus concentration.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a method for recovering a calcium phosphate fertilizer from sludge incineration bottom ash, which can effectively solve the problems that the extraction rate is low and new solid matters are generated in the extraction process to hinder the reaction in the existing method.

In order to achieve the purpose, the technical scheme adopted by the invention for solving the technical problems is as follows:

a method for recovering a calcium phosphate fertilizer from sludge incineration bottom ash comprises the following steps:

(1) drying the sludge incineration bottom ash to constant weight, and cooling to room temperature for later use;

(2) heating a hydrochloric acid solution with the concentration of 1.5-3.0 mol/L to 25-45 ℃, then mixing the hydrochloric acid solution with sludge incineration bottom ash in a liquid-solid ratio of less than or equal to 5mL/g, stirring at 50-400 rpm for 5-60 min, and filtering to obtain a phosphorus-rich extracting solution;

(3) adding calcium hydroxide into the phosphorus-rich extracting solution, reacting for 1-60 min, and then carrying out evaporation concentration on the reaction solution at 100-120 ℃ for 30-100 min to form a crystal film on the surface of the solution; the molar ratio of the calcium hydroxide to the phosphoric acid in the phosphorus-rich extracting solution is 0.5: 1-6: 1;

(4) and (4) naturally cooling and crystallizing the solution obtained in the step (3) at room temperature, filtering, collecting crystals on the upper part, and air-drying the crystals to obtain the phosphate fertilizer.

Furthermore, the volume-mass ratio of the hydrochloric acid solution to the sludge incineration bottom ash is 2-5 mL/g.

Further, the volume-mass ratio of the hydrochloric acid solution to the sludge incineration bottom ash is 3 mL/g.

Further, the concentration of the hydrochloric acid solution was 2.0 mol/L.

Further, the process of stirring and mixing the hydrochloric acid solution and the sludge incineration bottom ash comprises the following steps: stirring at 200rpm for 10min at room temperature.

Further, the molar ratio of calcium hydroxide to phosphoric acid in the phosphorus-rich extract was 2: 1.

Further, the reaction time of the calcium hydroxide and the phosphorus-rich extract is 30 min.

Further, the temperature of the evaporation concentration was 105 ℃ for 60 min.

Further, the sludge incineration bottom ash is the residual sludge incineration bottom ash after the residual sludge in the sewage plant is incinerated.

The extraction principle of this application does:

phosphorus-containing crystal Ca exists in sludge incineration bottom ash₁₉Fe₂(PO₄)₁₄During the treatment with hydrochloric acid, the following reaction occurs:

Ca₁₉Fe₂(PO₄)₁₄+38HCl+4H₂O＝＝19CaCl₂+2Fe(OH)₂+14H₃PO₄(1)

through the reaction, more than 90% of phosphorus can be extracted under the condition of sufficient hydrochloric acid and enters the phosphorus-rich extracting solution. Meanwhile, a large amount of calcium ions and chloride ions can be introduced into the extracting solution, so that the subsequent preparation of the calcium phosphate fertilizer is facilitated.

Then adding Ca (OH) into the extracting solution₂The reaction, which can generate phosphate fertilizer in the processes of evaporation, concentration, cooling and crystallization, comprises the following steps:

Ca(OH)₂+H₃PO₄+HCl＝＝CaClH₂PO₄·H₂O+H₂O (2)

evaporating under sufficient phosphorus, calcium and chloride ionsConcentrating, cooling for crystallization, filtering, and air drying to obtain calcium dihydrogen phosphate monohydrate (CaClH)₂PO₄·H₂O). Through carrying out surface element analysis on the phosphate fertilizer, the mass fraction of impurities is found to be lower than 0.01%, and the phosphate fertilizer can be used as a fertilizer for farmlands. And adding Ca (OH) separately₂The key points for obtaining the fertilizer are as follows: first, Ca (OH)₂Can provide calcium ions required by the calcium phosphate fertilizer; second, Ca (OH)₂Can introduce OH^-Neutralizing part H of the extract⁺So that the solution reaches the proper pH value to meet the requirement of the phosphate fertilizer CaClH₂PO₄·H₂And (4) the requirement of O crystallization.

The invention has the beneficial effects that:

1. the extraction rate of extracting phosphorus from sludge incineration bottom ash is generally high in the existing high liquid-solid ratio (20-150 mL/g), but the volume of the obtained phosphorus-rich extracting solution is large, which means that the phosphorus content in unit volume is low. If the phosphorus is recovered from the extracting solution, the phosphorus-rich extracting solution may need to be subjected to evaporation concentration treatment to obtain the extracting solution with high phosphorus content per unit volume, which causes cost increase and is not beneficial to large-scale application; if phosphorus can be recovered from the extract without evaporation, large volumes of waste liquid remain, which can be environmentally hazardous and temporarily without suitable disposal methods.

The method adopts a low liquid-solid ratio (the volume-mass ratio of the hydrochloric acid solution to the sludge incineration bottom ash is less than or equal to 5mL/g) for extraction, can achieve a good phosphorus-rich effect while extracting phosphorus, and has high phosphorus extraction rate and high phosphorus content in the unit volume of the obtained extracting solution. Compared with the high liquid-solid ratio, the low liquid-solid ratio can not generate a large amount of waste liquid, the volume of a reactor required in the subsequent evaporation and concentration process is smaller, the evaporation time is shorter, and therefore the cost for preparing the phosphate fertilizer is reduced.

2. The method adopts the hydrochloric acid solution which is preheated and has the concentration of 1.5-3.0 mol/L for extraction, and the preheated hydrochloric acid solution can reach the required temperature at the moment of contact with the sludge incineration bottom ash so as to react and quickly extract phosphorus in the bottom ash;

meanwhile, the hydrochloric acid with the concentration can perform various reactions with the sludge incineration bottom ash to extract most of phosphorus, so that a higher phosphorus extraction rate is obtained. If the concentration is too low, such as 0.5mol/L, the phosphorus extraction effect is not good, and the phosphorus extraction rate is only about 20.0 percent at most; if the concentration is too high, the phosphorus extraction effect is good, but a large amount of hydrochloric acid is wasted. Moreover, when the extraction is carried out by hydrochloric acid, new solid matters are not generated to hinder the extraction process.

3. This application still used calcium hydroxide in the preparation process, it not only can provide the calcium ion in the calcium phosphate fertilizer, can also provide the hydroxyl ion. The hydroxyl ions can be neutralized with the hydrogen ions in the phosphorus-rich extracting solution to increase the pH value of the solution, so that the phosphate fertilizer monohydrate calcium dihydrogen phosphate (CaClH) can be generated₂PO₄·H₂O) optimum crystallization conditions.

4. The extraction method of the invention takes the residual sludge incineration bottom ash of the sewage treatment plant as the raw material, and the extraction of phosphate rock can be reduced by taking the residual sludge incineration bottom ash as the raw material, thereby avoiding large-scale ecological damage, avoiding complex pretreatment, reducing the extraction difficulty, realizing the reutilization of the sludge incineration bottom ash, and avoiding the environmental pollution caused by improper treatment of the sludge incineration bottom ash.

Detailed Description

The following description of the embodiments of the present invention is provided to facilitate the understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention as defined and defined in the appended claims, and all matters produced by the invention using the inventive concept are protected.