阅读说明：本技术 除钼渣回收处理方法 (Molybdenum-removing slag recovery processing method ) 是由 漆辉杏 陈杰 王海军 于 2020-05-07 设计创作，主要内容包括：本发明涉及化工领域,具体涉及一种除钼渣回收处理方法。所提供的方法包括：(1)除钼渣加水配制第一料浆,与碱性溶液混合加热,反应,过滤得到第一滤液和第一滤渣；(2)调节第一滤液的pH值为弱碱性,加入双氧水反应,过滤得到第二滤液和第二滤渣；第一滤渣中加酸溶液配制第二料浆,与双氧水混合加热反应,过滤得到第三滤液和第三滤渣；(3)基于第二滤液进行离子交换处理,以便回收钨和钼；基于第三滤液进行结晶处理,以便获得硫酸铜和未结晶母液,未结晶母液返回步骤(2)第二料浆中重复利用；第二滤渣和第三滤渣进行热熔处理,以便回收硫。所提供的方法能实现除钼渣中有价元素的全面回收,且环保易操作,具有极高的经济效益。(The invention relates to the field of chemical industry, in particular to a method for recycling molybdenum-removing slag. The provided method comprises the following steps: (1) adding water to the molybdenum-removing residues to prepare first slurry, mixing the first slurry with an alkaline solution, heating, reacting, and filtering to obtain first filtrate and first filter residues; (2) adjusting the pH value of the first filtrate to be alkalescent, adding hydrogen peroxide for reaction, and filtering to obtain a second filtrate and second filter residue; adding an acid solution into the first filter residue to prepare second slurry, mixing the second slurry with hydrogen peroxide, heating for reaction, and filtering to obtain a third filtrate and third filter residue; (3) performing an ion exchange treatment based on the second filtrate to recover tungsten and molybdenum; crystallizing the third filtrate to obtain copper sulfate and an uncrystallized mother liquor, and returning the uncrystallized mother liquor to the second slurry in the step (2) for recycling; and carrying out hot melting treatment on the second filter residue and the third filter residue so as to recover sulfur. The method can realize comprehensive recovery of valuable elements in the molybdenum-removing slag, is environment-friendly and easy to operate, and has extremely high economic benefit.)

1. The method for recycling the molybdenum-removing slag is characterized by comprising the following steps:

(1) adding water to the molybdenum-removing residues to prepare first slurry, mixing the first slurry with an alkaline solution, heating, reacting, and filtering to obtain first filtrate and first filter residues;

(2) adjusting the pH value of the first filtrate to be alkalescent, adding hydrogen peroxide for reaction, and filtering to obtain a second filtrate and second filter residue;

adding an acid solution into the first filter residue to prepare second slurry, mixing the second slurry with hydrogen peroxide, heating for reaction, and filtering to obtain third filtrate and third filter residue;

(3) performing an ion exchange treatment based on the second filtrate to recover tungsten and molybdenum;

performing crystallization treatment based on the third filtrate so as to obtain copper sulfate and an uncrystallized mother liquor, wherein the uncrystallized mother liquor is returned to the second slurry in the step (2) for recycling;

and carrying out hot melting treatment on the basis of the second filter residue and the third filter residue so as to recover sulfur.

2. The method according to claim 1, wherein the alkaline solution of step (1) is a sodium hydroxide solution or a potassium hydroxide solution;

optionally, the alkaline solution is a sodium hydroxide solution, wherein the addition amount of sodium hydroxide is calculated according to the following formula:

the amount of sodium hydroxide added is 0.3 tungsten (1.2 to 1.5) +0.8 molybdenum (1.2 to 1.5).

3. The method according to claim 1, wherein the pH value of the first filtrate in the step (2) is adjusted to 7.5-9;

optionally, a diluted acid solution is added in the step (2) to adjust the pH of the first filtrate to be weakly alkaline, wherein the diluted acid solution comprises at least one selected from sulfuric acid, hydrochloric acid or nitric acid.

4. The method according to claim 1, wherein the amount of the hydrogen peroxide added to the first filtrate in the step (2) is calculated according to the following formula:

the amount of hydrogen peroxide is (mass of sulfur-0.5 mass of copper) ((2.5-3)).

5. The method according to claim 1, wherein the amount of hydrogen peroxide added to the second slurry in step (2) is calculated according to the following formula:

the amount of hydrogen peroxide was 6.4 × by mass of copper.

6. The method according to claim 1, wherein the liquid-solid mass ratio of the first slurry in the step (1) is 3-5: 1;

optionally, the liquid-solid mass ratio of the second slurry in the step (2) is 4-10: 1.

7. the method according to claim 1, wherein the alkaline solution is mixed and heated to 70-90 ℃ in step (1), and optionally the reaction time in step (1) is 1-3 hours.

8. The method according to claim 1, wherein the second slurry in the step (2) is mixed with hydrogen peroxide and heated to 40-60 ℃; optionally, in the step (2), the second slurry and hydrogen peroxide are mixed and heated for 2-5 hours.

9. The method of claim 1, wherein the recovery of tungsten and molybdenum is greater than 95%, the recovery of copper is greater than 95%, and the recovery of sulfur is greater than 85%.

10. A method for recovering valuable elements from molybdenum-removing slag is characterized by comprising the following steps:

(1) adding water to the molybdenum-removing residues to prepare first slurry, mixing the first slurry with sodium hydroxide, heating to 70-90 ℃, reacting, and filtering to obtain first filtrate and first filter residues;

(2) adjusting the pH value of the first filtrate to 7.5-9, adding hydrogen peroxide for reaction, and filtering to obtain a second filtrate and a second filter residue;

adding an acid solution into the first filter residue to prepare a second slurry, adding hydrogen peroxide, mixing, heating to 40-60 ℃, reacting, and filtering to obtain a third filtrate and a third filter residue;

(3) performing an ion exchange treatment based on the second filtrate to recover tungsten and molybdenum;

performing crystallization treatment based on the third filtrate so as to obtain copper sulfate and an uncrystallized mother liquor, wherein the uncrystallized mother liquor is returned to the second slurry in the step (2) for recycling;

and carrying out hot melting treatment on the basis of the second filter residue and the third filter residue so as to recover sulfur.

Technical Field

The invention relates to the field of chemical industry, in particular to a method for recycling molybdenum-removing slag.

Background

The molybdenum-removing slag is tungsten concentrate in situA waste material produced by removing molybdenum in the course of producing tungsten product, its main component is Cu₂MoS₄In addition, a small amount of WO remains₃And ammonium salts, basic. According to the national records of dangerous waste, which are recorded from 8.1.2016, molybdenum removal slag is identified as dangerous waste.

The treatment of the molybdenum removing slag is always a difficult problem for the research of metallurgy and chemical workers. At present, the domestic methods for treating the molybdenum-removing slag comprise the following steps: firstly, roasting the molybdenum-removing slag to remove sulfur, then carrying out alkaline leaching to separate copper, introducing molybdenum and tungsten into the solution in the form of sodium salt, and then carrying out evaporation crystallization to produce crude sodium molybdate. The sulfur dioxide generated by roasting in the method seriously pollutes the air, and the production environment is severe; one is directly alkaline leaching molybdenum slag, copper is left in the slag, tungsten enters solution in the form of sodium tungstate, molybdenum enters solution in the form of sodium thiomolybdate, and then, the solution is acidified by adding acid to convert thiomolybdate into molybdenum trisulfide precipitate to be separated from tungsten. The method generates highly toxic gas H in the acidification process₂S, polluting the environment; one is that after molybdenum slag is removed by alkaline leaching, Cu (OH) is added into alkaline leaching solution₂And combining S ions in the thiomolybdate, and then carrying out the next step of recycling the tungsten-molybdenum mixed solution. The method needs to add a large amount of copper hydroxide, so that the cost is high, the amount of copper slag is increased, and the recovery cost is greatly increased; one is to add concentrated sulfuric acid and sodium chlorate solution, remove molybdenum slag by oxidation with the strong oxidizing property of the concentrated sulfuric acid and the sodium chlorate, and then carry out the next recovery. The method adopts concentrated sulfuric acid for direct leaching, the operating environment is severe, sodium chlorate is unstable, potential safety hazards exist in the storage and use processes, and the method does not belong to a green oxidant.

Therefore, a new method for treating the molybdenum-removing slag meeting the environmental protection requirement is developed, valuable elements in the molybdenum-removing slag can be recovered, and the method becomes a problem to be solved urgently in the industry.

Disclosure of Invention

At least one object of the invention is to provide a method for recovering and treating molybdenum-removing slag, which is suitable for comprehensively recovering valuable elements from the molybdenum-removing slag. And the cost is low, and the environment is protected.

When the inventor of the invention recovers valuable elements in the molybdenum-removing slag, the traditional sulfur removal thought in molybdenum-removing slag treatment is changed, the process route of wet-method molybdenum-removing slag treatment is redesigned, and the problems that the traditional process does not meet the environmental protection requirement and the production environment is severe are solved. Meanwhile, valuable elements in the molybdenum-removing slag are comprehensively recovered, the recovery rate of tungsten and molybdenum can reach more than 95%, the recovery rate of copper is more than 95%, the recovery rate of sulfur is more than 85%, the process is simple, the cost is low, the operation is easy, and the method is applied to industry, such as the field of metallurgy and has extremely high economic benefit.

Specifically, the invention provides the following technical scheme:

in a first aspect of the invention, the invention provides a molybdenum-removing slag recovery processing method, which comprises the following steps: (1) adding water to the molybdenum-removing residues to prepare first slurry, mixing the first slurry with an alkaline solution, heating, reacting, and filtering to obtain first filtrate and first filter residues; (2) adjusting the pH value of the first filtrate to be alkalescent, adding hydrogen peroxide for reaction, and filtering to obtain a second filtrate and second filter residue; adding an acid solution into the first filter residue to prepare a second slurry, mixing the second slurry with hydrogen peroxide, heating for reaction, and filtering to obtain a third filtrate and a third filter residue; (3) performing an ion exchange treatment based on the second filtrate to recover tungsten and molybdenum; performing a crystallization treatment based on the third filtrate to obtain copper sulfate and an uncrystallized mother liquor, the uncrystallized mother liquor being recycled with the second slurry in step (2); and carrying out hot melting treatment on the basis of the second filter residue and the third filter residue so as to recover sulfur.

The molybdenum-removing slag contains copper, molybdenum, sulfur, WO3 and the like, and in order to recover valuable elements in the molybdenum-removing slag, water is added into the molybdenum-removing slag to prepare first slurry, then alkaline solution is added into the first slurry, and the first slurry is heated, so that molybdenum, sulfur, tungsten and the like in the molybdenum-removing slag react with the alkaline solution to obtain corresponding salts, for example, the salts can react with sodium hydroxide to generate Na₂MoS₄、Na₂WO₄、Na₂S, filtering to obtain a first filtrate and a first filter residue, wherein the first filtrate contains soluble salt and alkaline solution, and the main components of the first filter residue are CuS and Cu (OH)₂. The pH of the first filtrate obtained is adjusted to a slightly alkaline pH, which may be 7, for exampleAnd 5-9, slowly adding hydrogen peroxide, reacting, filtering to obtain a second filtrate and a second filter residue, wherein in the reaction process, the sulfur element is reduced to a simple substance, so that the simple substance sulfur is separated in the form of the filter residue (namely the second filter residue), the second filtrate mainly contains soluble salts of molybdenum and tungsten, and the tungsten and the molybdenum can be recovered through ion exchange treatment subsequently. The first filter residue can be added with acid to prepare slurry, hydrogen peroxide is slowly added, heating and reaction are carried out, a third filtrate and a third filter residue are obtained through filtering, in the reaction process, sulfur element in the first filter residue is separated out in the form of elemental sulfur, the third filter residue is formed, and the formed third filter residue inevitably contains a small amount of un-decomposed CuS besides the elemental sulfur. The third filtrate formed had the main components of CuSO4 and the previously added acid. And crystallizing the third filtrate to obtain copper sulfate, and mixing the residual mother liquor which is not crystallized with the second slurry for reuse. And the second filter residue and the third filter residue containing the elemental sulfur can be subjected to hot melting treatment so as to recover the sulfur.

By adopting the method provided by the invention, the molybdenum-removing slag is treated, and the problems that the traditional process does not meet the environmental protection requirement and the production environment is severe are solved. But also can realize the comprehensive recovery of valuable elements in the molybdenum-removing slag, can realize the recovery rate of tungsten and molybdenum to be more than 95 percent, the recovery rate of copper to be more than 95 percent and the recovery rate of sulfur to be more than 85 percent, has simple process, low cost and easy operation, is applied to industry, such as the field of metallurgy, and has extremely high economic benefit.

According to the embodiment of the invention, the recovery processing method of the molybdenum-removing slag further comprises the following technical characteristics:

the alkaline solution used in step (1) may be a commonly used alkaline solution. But the alkaline solution may be sodium hydroxide or potassium hydroxide based on industrial cost considerations. The adding amount of the sodium hydroxide is calculated according to the following formula: the amount of sodium hydroxide added is 0.3 tungsten (1.2 to 1.5) +0.8 molybdenum (1.2 to 1.5). The content of tungsten and the content (percentage content) of molybdenum can be directly detected and analyzed by molybdenum removal slag. And then calculating the total mass of the tungsten and the molybdenum according to the detection result and the weight of the added molybdenum-removing slag. Wherein the mass of the added sodium hydroxide (note that the sodium hydroxide is not the sodium hydroxide solution) can be calculated by the formula of adding 0.3 tungsten mass (1.2-1.5) +0.8 molybdenum mass (1.2-1.5), wherein "0.3 tungsten mass" in the formula refers to the theoretical amount of sodium hydroxide required for the sodium hydroxide to fully react with tungsten in the molybdenum-removing slag to obtain the sodium tungstate solution, and for the full reaction, the sodium hydroxide has an excess coefficient on the theoretical basis, and "1.2-1.5" refers to the excess coefficient of the sodium hydroxide. The latter half of the formula is also obtained based on the same idea for the reaction of molybdenum.

In some embodiments of the present invention, the pH of the first filtrate in the step (2) is adjusted to 7.5 to 9. The pH value of the first filtrate is very critical, if the feed liquid is adjusted to be acidic, hydrogen ions are combined with negative divalent sulfur to obtain hydrogen sulfide highly toxic gas, so in order to ensure that the hydrogen sulfide highly toxic gas is not generated in the acid adding process, the acid is slowly added to avoid local peracid, and in addition, the pH value of the end-point feed liquid is ensured to be more than or equal to 7.5 (theoretically more than or equal to 7, but the pH value is increased to 7.5 for the sake of safety), and the generation of hydrogen sulfide gas is avoided. In addition, the oxidability of the hydrogen peroxide is strongest in neutral and weakly acidic feed liquid, so if the acid adjustment is not in place, for example, when the pH value is too high, the subsequent oxidability of the hydrogen peroxide is influenced. The higher the pH value is, the more hydrogen peroxide is consumed, and when the alkalinity reaches a certain degree, the hydrogen peroxide added into the feed liquid can perform neutralization reaction with excessive hydroxide ions, so that the feed liquid has no oxidation performance. In some embodiments of the present invention, the pH of the first filtrate is adjusted to be weakly alkaline by adding a dilute acid solution in step (2), wherein the dilute acid solution comprises at least one selected from sulfuric acid, hydrochloric acid or nitric acid. In this context, reference to dilute acid solutions is to be understood as referring to acidic solutions commonly used in the art, such as sulfuric acid, hydrochloric acid or nitric acid, and the like, but excluding concentrated hydrochloric acid, concentrated nitric acid, and the like. The use of these solutions facilitates the adjustment of the pH of the solution.

In some embodiments of the present invention, the amount of the hydrogen peroxide added to the first filtrate in the step (2) is calculated according to the following formula: the amount of hydrogen peroxide is (mass of sulfur-0.5 mass of copper) ((2.5-3)). The mass of copper and the mass of sulfur mentioned in the formula refer to the elemental content. And detecting the sulfur content and the copper content by utilizing the molybdenum removal slag. The purpose of adding hydrogen peroxide is mainly to oxidize negative divalent sulfur, copper after alkaline leaching mainly exists in the form of copper sulfide, the mass of sulfur in feed liquid after alkaline leaching is (the mass of sulfur is-0.5 copper mass), the content theory of hydrogen peroxide required by oxidation is (the mass of sulfur is-0.5 copper mass), and the hydrogen peroxide is multiplied by (2.5-3) as an excess coefficient because a small amount of decomposition inevitably exists in the oxidation process.

In some embodiments of the present invention, the amount of the hydrogen peroxide solution added to the slurry in the step (2) is calculated according to the following formula: the amount of hydrogen peroxide was 6.4 × by mass of copper. The purpose of adding hydrogen peroxide at this step is mainly to oxidize copper sulphide to copper sulphate, so the amount of hydrogen peroxide is determined mainly by the mass of copper, the theoretical amount being 4 x the mass of copper, and in addition, for the sake of full reaction, it was found through experiments that the leaching rate is highest when the ratio of the amount of hydrogen peroxide to the mass of copper is 6.4.

In addition, in both the first slurry and the second slurry, the higher the liquid-solid ratio is, the larger the liquid-solid contact area is, and the more sufficient the reaction is, but when the liquid-solid ratio is too large, the concentration of other substances to be added is also decreased accordingly, and the reaction is not favorable to some extent. According to research, in some embodiments of the invention, the liquid-solid mass ratio of the first slurry in the step (1) is 3-5: 1. In some embodiments of the invention, the liquid-solid mass ratio of the second slurry in the step (2) is 4-10: 1. this can promote the reaction.

In some embodiments of the present invention, the alkaline solution is mixed and heated to 70-90 ℃ in step (1). Under such temperature conditions, the salt-forming reaction can be promoted. In some embodiments of the present invention, the reaction time in step (1) is 1 to 3 hours. Thus, the reaction can be made complete and the corresponding salt solution obtained.

In some embodiments of the invention, after adding hydrogen peroxide to the second slurry in the step (2), heating to 40-60 ℃. This can promote the reaction. According to the embodiment of the invention, in the step (2), the second slurry and hydrogen peroxide are mixed and heated for reaction for 2-5 hours.

In some embodiments of the invention, the recovery of tungsten and molybdenum is above 95%, the recovery of copper is above 95%, and the recovery of sulfur is above 85%.

In a second aspect of the invention, the invention provides a method for recovering valuable elements from molybdenum removal slag, which comprises the following steps: (1) adding water to the molybdenum-removing residues to prepare first slurry, mixing the first slurry with a sodium hydroxide solution, heating to 70-90 ℃, reacting, and filtering to obtain first filtrate and first filter residues; (2) adjusting the pH value of the first filtrate to 7.5-9, adding hydrogen peroxide for reaction, and filtering to obtain a second filtrate and a second filter residue; adding an acid solution into the first filter residue to prepare a second slurry, adding hydrogen peroxide, mixing, heating to 40-60 ℃, reacting, and filtering to obtain a third filtrate and a third filter residue; (3) performing an ion exchange treatment based on the second filtrate to recover tungsten and molybdenum; performing crystallization treatment based on the third filtrate so as to obtain copper sulfate and an uncrystallized mother liquor, wherein the uncrystallized mother liquor is returned to the second slurry in the step (2) for recycling; and carrying out hot melting treatment on the basis of the second filter residue and the third filter residue so as to recover sulfur. By the method, valuable elements in the molybdenum-removing slag can be comprehensively recovered, and the problems that the traditional process does not meet the environmental protection requirement and the production environment is severe are solved. The method can realize the recovery rate of tungsten and molybdenum of more than 95 percent, the recovery rate of copper of more than 95 percent and the recovery rate of sulfur of more than 85 percent, has simple flow, low cost and easy operation, is applied to industry, such as the field of metallurgy, and has extremely high economic benefit.

Drawings

FIG. 1 is a method for recovering and treating molybdenum-removed slag according to an embodiment of the invention.

Detailed Description

The following detailed description of embodiments of the invention is intended to be illustrative, and is not to be construed as limiting the invention. Also, certain terms used herein are explained and illustrated to facilitate understanding by those skilled in the art, and it is to be understood that such explanation and illustration are only for convenience of understanding and should not be construed as limiting the scope of the present invention.

The invention provides a molybdenum-removing slag recovery processing method, which comprises the following steps: (1) adding water to the molybdenum-removing residues to prepare first slurry, mixing the first slurry with an alkaline solution, heating, reacting, and filtering to obtain first filtrate and first filter residues; (2) adjusting the pH value of the first filtrate to be alkalescent, adding hydrogen peroxide for reaction, and filtering to obtain a second filtrate and second filter residue; adding an acid solution into the first filter residue to prepare a second slurry, mixing the second slurry with hydrogen peroxide, heating for reaction, and filtering to obtain a third filtrate and a third filter residue; (3) performing an ion exchange treatment based on the second filtrate to recover tungsten and molybdenum; performing a crystallization treatment based on the third filtrate to obtain copper sulfate and an uncrystallized mother liquor, the uncrystallized mother liquor being recycled with the second slurry in step (2); and carrying out hot melting treatment on the basis of the second filter residue and the third filter residue so as to recover sulfur.

Before the molybdenum-removing slag is recycled, firstly, detecting copper, molybdenum, sulfur and WO in the molybdenum-removing slag₃And (4) content. Then, the molybdenum-removing slag can be prepared into a first slurry with a liquid-solid mass ratio of 3-5: 1 by adding water, and then an alkaline solution is added, wherein the alkaline solution is prepared by taking sodium hydroxide as an example. Then heating the solution to 70-90 ℃, stirring and reacting for 1-3 hours, and filtering to obtain a first filtrate and a first filter residue; wherein the first filtrate contains Na as main ingredient₂MoS₄、Na₂WO₄、Na₂S and NaOH; the main components of the first filter residue are CuS and Cu (OH)₂B, carrying out the following steps of; the sodium hydroxide is added in an amount of 0.3 tungsten by mass (1.2 to 1.5) +0.8 molybdenum by mass (1.2 to 1.5).

In at least some embodiments of the invention, dilute acid is slowly added to the first filtrate during stirring to adjust the pH of the first filtrate to 7.5-9. Cooling to room temperature, slowly adding hydrogen peroxide while stirring, stirring at room temperature for reaction for 1-2h, and filtering to obtain a second filtrate and a second filter residue; the second filtrate contains Na as main component₂MoO₄And Na₂WO₄(ii) a Of the second filter residueThe component is simple substance sulfur. The dilute acid is one or more of sulfuric acid, hydrochloric acid and nitric acid. The amount of hydrogen peroxide added is (mass of sulfur-0.5 mass of copper) × (2.5-3).

The second filtrate can be subjected to tungsten-molybdenum separation according to a conventional ion exchange method, for example, adsorption and desorption are performed through macroporous weak base anion exchange resin to obtain a sodium tungstate solution and a sodium molybdate solution, and the sodium tungstate solution and the sodium molybdate solution are returned to the tungsten smelting production process for use.

In at least some embodiments of the invention, dilute sulfuric acid is added into the obtained first filter residue to prepare second slurry with a liquid-solid mass ratio of 4: 1-10: 1, hydrogen peroxide is slowly added, the mixture is heated to 50 ℃, stirred and reacted for 2-5 hours, and a third filtrate and third filter residue are obtained by filtering. The concentration of the dilute sulfuric acid is 3-4 mol/L. Wherein the adding amount of the hydrogen peroxide is 6.4 times of the mass of the copper. The main component of the third filtrate is CuSO₄And dilute acids. The third filter residue comprises elemental sulfur and a small amount of un-decomposed CuS.

In at least some embodiments of the present invention, the elemental sulfur collected in the second and third filter residues is recovered by a conventional hot melt process. The collected elemental sulfur is recovered by a conventional hot melting method, the recovery yield is high, the residue amount is very small, and almost all the elemental sulfur can be recovered by the method. . Of course, in at least some embodiments of the present invention, the residue remaining after the conventional hot melt recovery process can also be returned to the first residue for recycling. Therefore, the recovery rate of sulfur can be improved, and the cost can be saved.

In at least some embodiments of the present invention, the third filtrate is crystallized by conventional evaporation cooling to obtain copper sulfate product, and the mother liquor without crystallization (i.e. the mother liquor remaining after crystallization) contains a small amount of copper sulfate solution as a main component of dilute acid, and can be recycled with the second slurry. Therefore, the recovery rate of copper can be improved, and the cost can be saved.

The scheme of the invention will be explained with reference to the examples. It will be appreciated by those skilled in the art that the following examples are illustrative of the invention only and should not be taken as limiting the scope of the invention. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.

For convenience of reading and distinguishing, the following examples are given by referring to filtrate a, residue a, filtrate B, residue B, filtrate C, residue C, etc. for different stages or differently treated filtrates and residues, respectively. These have the same meaning as the first filtrate, first residue, second filtrate, second residue, third filtrate, third residue, etc. mentioned herein, and are used for distinction only and not for representation of layers or to illustrate importance.