A method for preparing lithium phosphate from carbonate-type salt lake brine

Abstract

A method for preparing lithium phosphate from carbonate-type salt lake brine, comprising the following steps: (1) Pretreatment of raw brine: The carbonate-type salt lake brine is pre-sunned or evaporated and concentrated in a salt field to obtain lithium carbonate saturated brine; (2) Heating and aging: Phosphates are added to the lithium carbonate saturated brine, mixed evenly, heated and aged to obtain a slurry; (3) Solid-liquid separation, the slurry is subjected to solid-liquid separation, the solid is collected, and the solid is washed to obtain crude lithium phosphate solid; (4) Precipitating high-purity lithium phosphate: Deionized water is added to the crude lithium phosphate to prepare a slurry; then the slurry is heated, phosphoric acid is added to adjust the pH value of the slurry, and the lithium phosphate precipitation reaction is carried out. After the reaction, solid-liquid separation is carried out, and the solid is collected to obtain the lithium phosphate product. The process flow of the present invention is short, the operation is simple, the equipment used is simple, the requirements for equipment are low, the production cost is low, and it is suitable for large-scale popularization and use.

Description

Technical Field

[0001] The present invention relates to a method for preparing lithium phosphate from salt lake brine, in particular to a method for preparing lithium phosphate from carbonate type salt lake brine. Background Art

[0002] With the development of new energy vehicles, the demand for battery positive electrode materials has increased by leaps and bounds. Lithium iron phosphate is favored by many battery manufacturers due to its high safety factor and low price. As one of the raw materials of lithium iron phosphate, the demand for lithium phosphate is also increasing significantly. Therefore, the development of technology for directly preparing lithium phosphate from salt lake brine will have great economic value.

[0003] 80% of my country's lithium resources are stored in salt lake brines, among which carbonate salt lake brines are the most prominent. Due to its low magnesium-lithium ratio and mature development technology, there have been successful cases of carbonate salt lake brines being developed, such as the Zabuye Salt Lake in Tibet. However, the development of carbonate salt lakes also has disadvantages such as long production cycle, low yield and low product quality. This is mainly due to the presence of carbonate ions, which causes lithium carbonate to gradually precipitate during the production process of brine concentration. The use of lithium phosphate method to precipitate salt lake lithium can greatly improve the utilization rate of salt lake lithium resources.

[0004] CN 110357055 A discloses a method for extracting lithium from salt lake brine and preparing lithium phosphate, using excess oxalic acid as a precipitant to remove impurity metal ions such as calcium and magnesium in the salt lake brine to obtain a filtrate containing lithium ions, the phosphate radicals in the filtrate interact with the lithium ions, and microwave heating is combined to adjust the precipitation rate of lithium phosphate and pore formation, thereby obtaining nano-scale porous lithium phosphate. This method combines microwave heating technology, has high production costs, and is complex to operate, and is not suitable for large-scale production in lithium extraction from brine.

[0005] CN 112299451 A discloses a method for preparing lithium hydroxide from low-magnesium lithium-containing brine in the form of lithium phosphate. An inorganic alkaline compound is used to adjust the pH value of the low-magnesium lithium-containing brine to above 10 to precipitate calcium and magnesium, obtaining lithium-containing brine with calcium and magnesium removed; phosphoric acid solution is added for precipitation reaction. After the obtained lithium phosphate precipitate is centrifuged and washed, it is dissolved in phosphoric acid solution to obtain lithium dihydrogen phosphate solution; the lithium dihydrogen phosphate solution is purified and then subjected to bipolar membrane electrodialysis. The obtained lithium hydroxide solution is concentrated and crystallized to obtain lithium hydroxide product. This method is only applicable to brine with low calcium and magnesium content. For the lithium-containing brine after calcium and magnesium removal, an alkaline solution needs to be used. Due to its relatively high calcium and magnesium content, colloidal magnesium hydroxide and calcium hydroxide precipitates will form, which requires a large amount of alkali. These two precipitates have a high water content, making filtration and separation difficult, and resulting in a lithium entrainment loss of more than 30%. At the same time, using the alkaline solution has a relatively high production cost. In addition, after precipitating lithium phosphate in this method, phosphoric acid in phosphoric acid solution twice the equivalent amount of lithium phosphate precipitate needs to be added to form lithium dihydrogen phosphate solution. The added phosphoric acid with a mass fraction of 8.7% has a relatively low concentration. The lithium dihydrogen phosphate solution is successively subjected to plate and frame filtration, multi-media filtration, ultrafiltration and resin adsorption. After purification, bipolar membrane electrodialysis is carried out to obtain lithium hydroxide solution and phosphoric acid solution. Its raw material phosphoric acid has a large addition amount, the process is long, and at the same time, the energy consumption is large and lithium needs to go through multiple processes, resulting in a low lithium recovery rate. Moreover, carbonate-type salt lake brine mainly exists in Tibet region of China, and the environmental protection policy is relatively strict. Phosphoric acid and strong alkali are less applicable for precipitating lithium phosphate in Tibet region. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the above-mentioned defects existing in the prior art and provide a method for preparing lithium phosphate from carbonate-type salt lake brine with simple process and low production cost.

[0007] The technical solution adopted by the present invention to solve its technical problem is a method for preparing lithium phosphate from carbonate-type salt lake brine, comprising the following steps:

[0008] (1) Pretreatment of raw brine: The carbonate-type salt lake brine is pre-sunned or evaporated and concentrated in a salt field to obtain lithium carbonate saturated brine;

[0009] (2) Heating and aging: Phosphate is added to the lithium carbonate saturated brine obtained in step (1), mixed evenly, heated and aged to obtain a slurry;

[0010] (3) Solid-liquid separation: The slurry obtained in step (2) is subjected to solid-liquid separation, the solid is collected, and the solid is washed to obtain crude lithium phosphate solid;

[0011] (4) Precipitating high-purity lithium phosphate: Deionized water is added to the crude lithium phosphate obtained in step (3) to prepare a slurry; then the slurry is heated, phosphoric acid is added to adjust the pH value of the slurry, and a reaction for precipitating lithium phosphate is carried out. After the reaction, solid-liquid separation is carried out, and the solid is collected to obtain lithium phosphate product.

[0012] Further, in step (1), the carbonated salt lake brine refers to the brine in which the concentrations of carbonate and bicarbonate ions exceed those of calcium and magnesium ions; the sum of the concentrations of carbonate ions and bicarbonate ions in the carbonated salt lake brine is ≥ 5 g / L, and the concentration of lithium ions is ≥ 0.1 g / L.

[0013] Further, in step (1), the concentration of carbonate ions in the saturated lithium carbonate brine is ≥ 20 g / L, and the concentration of lithium ions is ≥ 1.0 g / L.

[0014] The purpose of step (1) is to concentrate lithium carbonate in the brine. At the same time, a large amount of impurity salts (such as NaCl, KCl, Na2SO4, etc.) are precipitated, reducing the amount of water for subsequent treatment, simplifying the process flow, increasing the system yield of lithium ions, and reducing production costs.

[0015] Further, in step (2), the phosphate is a non-strongly basic phosphate, preferably one or more of disodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium phosphate; the addition amount of the phosphate is 50 - 300% of the molar amount of lithium in the saturated lithium carbonate brine.

[0016] Further, in step (2), the temperature for heating and aging is 70 - 100 °C; the time for heating and aging is 10 - 200 minutes. If the temperature is too high, the energy consumption increases, and at the same time, microcrystals are easily formed, and it is easy to pass through the filter during filtration, reducing the product yield and easily forming other impurity ions to reduce the product grade; if the temperature is too low, the precipitation of lithium ions is incomplete, and the lithium ion yield is low. In addition, sufficient heating and conversion time is also to make the reaction complete and increase the lithium ion yield.

[0017] The purpose of heating and aging in step (2) is to increase the reaction yield and particle growth, facilitating subsequent separation. If this step is omitted and step (4) is directly carried out, the product yield will be reduced by at least more than 10%, and it will cause filtration difficulties.

[0018] Further, in step (3), the crude lithium phosphate contains 10 - 30 wt% lithium carbonate.

[0019] Further, in step (4), the solid-liquid ratio of the crude lithium phosphate to deionized water in the slurry is 1:1 - 3. If the solid-liquid ratio is too high, the amount of water added is large, the amount of heating treatment at the back end is large and the energy consumption is high, and at the same time, a part of lithium phosphate is dissolved in water, reducing the lithium ion yield; if the solid-liquid ratio is too low, the impurity removal is incomplete, and the purity of the lithium phosphate product is low.

[0020] Further, in step (4), the pH value is 1 to 4. If the pH value is lower than 1, it will be converted into lithium hydrogen phosphate, while if the pH value is higher than 4, lithium hydroxide will be produced. Controlling the pH value range can inhibit the formation of these two products, ensuring that the precipitated lithium mainly exists in the form of lithium phosphate, and reducing the subsequent refining cost of lithium phosphate.

[0021] Further, in step (4), the temperature of the reaction is 70 to 100 °C; the reaction time is 5 to 300 minutes. Similarly, if the temperature is too high, the energy consumption increases, and at the same time, microcrystals are easily formed, and it is easy to pass through the filter during filtration, reducing the product yield and easily forming other impurity ions to reduce the product grade; if the temperature is too low, the precipitation of lithium ions is incomplete, and the yield of lithium ions is low.

[0022] Further, in step (4), the lithium phosphate product is a battery-grade lithium phosphate product.

[0023] Further, in steps (3) and (4), after washing the solid, collect the mother liquor and brine from the solid-liquid separation, add 105 to 110% of CaCl2 based on the total molar amount of phosphate radicals in the mother liquor and brine, react for 30 to 100 minutes, and then perform solid-liquid separation to obtain calcium hydrogen phosphate solid and brine with a phosphate radical content ≤ 0.005 g / L. Return the obtained brine to the lake for recycling.

[0024] The main reactions involved in the present invention are as follows:

[0025] 5Li + +PO4 3- +CO3 2- →Li2CO3+Li3PO4 (heating up)

[0026] 2Li2CO3+Li3PO4+2H3PO4→3H2O+2CO2+3Li3PO4 (refining)

[0027] 2PO4 3 +3Ca 2+ →Ca3(PO4)2 (phosphorus removal)

[0028] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention solves the problem of non-enrichment of lithium in carbonate-type brine, has a short process flow, is easy to operate, uses simple equipment, has low requirements for equipment, low production cost, and is suitable for large-scale popularization and use. Specific embodiments

[0029] The present invention will be further described below with reference to specific embodiments. These embodiments shall not be used to interpret the limitation of the scope of protection requested by the claims of this application. Based on the embodiments of the present invention, all other changes or modifications obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the claims of this application.

[0030] For the purity detection of lithium phosphate obtained in each example, the method specified in the current national standard (GB / T 11075-2003) was used for detection.

[0031] Example 1

[0032] (1) Pretreatment of raw brine: The brine raw material in this example is the brine of a severely carbonate-type salt lake in Tibet, China, in which the mass concentration of CO3 2- is 31.2 g / L, and the mass concentration of Li + is 0.70 g / L. After pre-sunning in the salt pan, a lithium carbonate saturated brine with a CO3 2- mass concentration of 67.3 g / L and a Li + mass concentration of 2.01 g / L is obtained;

[0033] (2) Temperature rise and aging: Sodium dihydrogen phosphate is added to the lithium carbonate saturated brine obtained in step (1). The addition amount of sodium dihydrogen phosphate is 105% of the molar amount of Li + in the lithium carbonate saturated brine. Stir and mix evenly, slowly heat up to 90 °C, and age for 60 minutes to obtain a slurry;

[0034] (3) Solid-liquid separation: Filter and separate the slurry obtained in step (2), collect the solid, and wash the solid to obtain a crude lithium phosphate solid. The washing mother liquor and the mother liquor from the filter separation enter step (5);

[0035] (4) Precipitate high-purity lithium phosphate: Add deionized water to the crude lithium phosphate obtained in step (3) to prepare a slurry with a solid-liquid ratio of 1:1; then heat the slurry to 80 °C, add phosphoric acid to adjust the pH value of the slurry to 3, and continue to maintain the lithium phosphate precipitation reaction at 80 °C for 120 minutes. After the reaction, perform solid-liquid separation, collect the solid, wash the solid, and dry it at 180 °C to obtain a lithium phosphate product;

[0036] (5) In steps (3) and (4), after washing the solid, collect the mother liquor and brine from the solid-liquid separation, add 105% CaCl2 of the total molar amount of phosphate in the mother liquor and brine, react for 30 minutes, and then perform solid-liquid separation to obtain calcium hydrogen phosphate solid and brine with a phosphate content of 0.003 g / L. The obtained brine is returned to the lake for recycling.

[0037] After detection, the lithium phosphate product obtained in step (4) is battery-grade lithium phosphate, in which Li + is 17.92%, PO4 3- is 26.76%, the lithium precipitation yield after concentration is 87.22%, and the purity of lithium phosphate is 99.68%

[0038] Example 2

[0039] (1) Pretreatment of raw brine: The brine raw material in this example is the brine of a severely carbonate-type salt lake in Tibet, China, where the mass concentration of CO3 2- is 15.3 g / L, and the mass concentration of Li + is 0.53 g / L. After pre-sunning in the salt pan, a lithium carbonate saturated brine with a CO3 2- mass concentration of 53.6 g / L and a Li + mass concentration of 2.56 g / L is obtained;

[0040] (2) Heating and aging: Sodium phosphate is added to the lithium carbonate saturated brine obtained in step (1). The addition amount of sodium phosphate is 110% of the molar amount of Li + in the lithium carbonate saturated brine. Stir and mix evenly, slowly heat up to 80 °C, and age for 120 minutes to obtain a slurry;

[0041] (3) Solid-liquid separation: The slurry obtained in step (2) is filtered and separated, the solid is collected, and the solid is rinsed to obtain crude lithium phosphate solid. The rinsing mother liquor and the filtration separation mother liquor enter step (5);

[0042] (4) Precipitating high-purity lithium phosphate: Deionized water is added to the crude lithium phosphate obtained in step (3) to prepare a slurry with a solid-liquid ratio of 1:2; then the slurry is heated to 70 °C, phosphoric acid is added to adjust the pH value of the slurry to 2, and the lithium phosphate precipitation reaction is continued at 70 °C for 180 minutes. After the reaction, solid-liquid separation is carried out, the solid is collected, the solid is washed, and dried at 200 °C to obtain lithium phosphate product;

[0043] (5) In steps (3) and (4), after washing the solid, the mother liquor and brine of the solid-liquid separation are collected, 100% CaCl2 of the total phosphate root molar amount in the mother liquor and brine is added, reacted for 30 minutes, and then solid-liquid separation is carried out to obtain calcium hydrogen phosphate solid and brine with a phosphate root content of 0.004 g / L. The obtained brine is returned to the lake for recycling.

[0044] After testing, the lithium phosphate product obtained in step (4) is battery-grade lithium phosphate, where Li + is 17.96%, PO4 3- is 26.95%, the lithium precipitation yield after concentration is 90.17%, and the purity of lithium phosphate is 99.90%.

[0045] Example 3

[0046] (1) Pretreatment of raw brine: The brine raw material in this example is the brine of a severely carbonate-type salt lake in Tibet, China, where the mass concentration of CO3 2- is 20.1 g / L, and the mass concentration of Li + is 0.22 g / L. After pre-sunning in the salt pan, a CO3 2- with a mass concentration of 47.3 g / L and Li+ Lithium carbonate saturated brine with a mass concentration of 1.89 g / L;

[0047] (2) Heating and aging: Sodium hydrogen phosphate is added to the lithium carbonate saturated brine obtained in step (1). The addition amount of sodium hydrogen phosphate is 100% of the molar amount of Li in the lithium carbonate saturated brine. Stir and mix evenly, slowly heat up to 100 °C, and age for 30 minutes to obtain a slurry; + The addition amount of sodium hydrogen phosphate is 100% of the molar amount of Li in the lithium carbonate saturated brine. Stir and mix evenly, slowly heat up to 100 °C, and age for 30 minutes to obtain a slurry;

[0048] (3) Solid-liquid separation: Filter and separate the slurry obtained in step (2), collect the solid, wash the solid to obtain crude lithium phosphate solid. The washing mother liquor and the filtration separation mother liquor enter step (5);

[0049] (4) Precipitating high-purity lithium phosphate: Deionized water is added to the crude lithium phosphate obtained in step (3) to prepare a slurry with a solid-liquid ratio of 1:3; then heat the slurry to 90 °C, add phosphoric acid to adjust the pH value of the slurry to 1, continue to maintain the lithium phosphate precipitation reaction at 90 °C for 30 minutes. After the reaction, perform solid-liquid separation, collect the solid, wash the solid, and dry it at 250 °C to obtain lithium phosphate product;

[0050] (5) In steps (3) and (4), after washing the solid, collect the mother liquor and brine from the solid-liquid separation, add 110% CaCl2 of the total molar amount of phosphate radicals in the mother liquor and brine, react for 90 minutes, and then perform solid-liquid separation to obtain calcium hydrogen phosphate solid and brine with a phosphate radical content of 0.002 g / L. The obtained brine is returned to the lake for recycling.

[0051] After testing, the lithium phosphate product obtained in step (4) is battery-grade lithium phosphate, in which Li + is 17.95%, PO4 3- is 26.93%. The lithium precipitation yield of concentrated lithium ions is 85.70%, and the purity of lithium phosphate is 99.85%.

[0052] Comparative Example 1

[0053] Compared with Example 2, the main difference is that Comparative Example 1 does not have the heating and aging step in step (2).

[0054] (1) Pretreatment of raw brine: The brine raw material in this example is a severely carbonate-type salt lake brine in a certain place in Tibet, China. The mass concentration of CO3 2- is 15.3 g / L, and the mass concentration of Li + is 0.53 g / L. After pre-sunning in the salt field, lithium carbonate saturated brine with a CO3 2- mass concentration of 53.6 g / L and a Li + mass concentration of 2.56 g / L is obtained;

[0055] (2) To the saturated lithium carbonate brine obtained in step (1), add phosphoric acid to adjust the pH value to 2, and carry out the lithium phosphate precipitation reaction at room temperature for 180 minutes. After the reaction, perform solid-liquid separation, collect the solid, wash the solid, and dry it at 200 °C to obtain the lithium phosphate product.

[0056] After testing, the obtained lithium phosphate product is Li + with a content of 13.46% and PO4 3- with a content of 20.80% crude lithium phosphate. The lithium precipitation yield after concentration is 45%, and the purity of lithium phosphate is 73%.

[0057] Comparative Example 2

[0058] Compared with Example 2, the main difference is that the process parameters in Comparative Example 2 are different.

[0059] (1) Pretreatment of raw brine: The brine raw material in this example is a severely carbonate-type salt lake brine in a certain place in Tibet, China. The mass concentration of CO3 2- is 15.3 g / L, and the mass concentration of Li + is 0.53 g / L. After pre-sunning in the salt field, a saturated lithium carbonate brine with a CO3 2- mass concentration of 53.6 g / L and a Li + mass concentration of 2.56 g / L is obtained;

[0060] (2) Heating and aging: Add sodium phosphate to the saturated lithium carbonate brine obtained in step (1). The addition amount of sodium phosphate is 110% of the molar amount of Li + in the saturated lithium carbonate brine. Stir and mix evenly, slowly heat up to 110 °C, and age for 120 minutes to obtain a slurry;

[0061] (3) Solid-liquid separation: Filter and separate the slurry obtained in step (2), collect the solid, and wash the solid to obtain the crude lithium phosphate solid. The washing mother liquor and the filtration separation mother liquor enter step (5);

[0062] (4) Precipitating high-purity lithium phosphate: Add deionized water to the crude lithium phosphate obtained in step (3) to prepare a slurry with a solid-liquid ratio of 1:4; then heat the slurry to 80 °C, add phosphoric acid to adjust the pH value of the slurry to 2, continue to maintain the lithium phosphate precipitation reaction at 80 °C for 180 minutes. After the reaction, perform solid-liquid separation, collect the solid, wash the solid, and dry it at 200 °C to obtain the lithium phosphate product;

[0063] (5) In steps (3) and (4), after washing the solid, collect the mother liquor and brine from the solid-liquid separation, add 100% CaCl2 of the total phosphate root molar amount in the mother liquor and brine, react for 30 minutes, and then perform solid-liquid separation to obtain calcium hydrogen phosphate solid and brine with a phosphate root content of 0.004 g / L. Return the obtained brine to the lake for recycling.

[0064] After detection, due to the high aging temperature, microcrystals are easily formed, making it difficult to filter in step (3), and easy to have filtrate leakage during filtration. In the lithium phosphate product obtained in step (4), the content of Li + is 16.35%, and the content of PO4 3- is 25.63%. The lithium precipitation yield of concentrated lithium ions is 83.67%, and the purity of lithium phosphate is 99.63%.

Claims

1. A method for preparing lithium phosphate from carbonate-type salt lake brine, characterized in that, It includes the following steps: (1) Pretreatment of raw brine: Pre-sun or evaporate and concentrate the carbonate-type salt lake brine in a salt pan to obtain lithium carbonate saturated brine; the carbonate-type salt lake brine is brine in which the concentrations of carbonate and bicarbonate ions exceed those of calcium and magnesium ions; (2) Heating and aging: Add phosphate to the lithium carbonate saturated brine obtained in step (1), mix evenly, heat and age to obtain a slurry; the phosphate is a non-strongly basic phosphate; (3) Solid-liquid separation: Perform solid-liquid separation on the slurry obtained in step (2), collect the solid, wash the solid to obtain a crude lithium phosphate solid; (4) Precipitating high-purity lithium phosphate: Add deionized water to the crude lithium phosphate obtained in step (3) to prepare a slurry, and the solid-liquid ratio of the crude lithium phosphate to deionized water in the slurry is 1:1 to 3; then heat the slurry, add phosphoric acid to adjust the pH value of the slurry to 1-4, and carry out the lithium phosphate precipitation reaction. The temperature of the reaction is 70-100 °C, and the reaction time is 5-300 minutes; after the reaction, perform solid-liquid separation, collect the solid, and obtain the lithium phosphate product.

2. The method for preparing lithium phosphate from carbonated salt lake brine according to claim 1, wherein In step (1), the sum of the concentrations of carbonate ions and bicarbonate ions in the carbonate-type salt lake brine ≥ 5 g / L, and the concentration of lithium ions ≥ 0.1 g / L.

3. The method for preparing lithium phosphate from carbonate-type salt lake brine according to claim 1 or 2, characterized in that, In step (1), the concentration of carbonate ions in the lithium carbonate saturated brine ≥ 20 g / L, and the concentration of lithium ions ≥ 1.0 g / L.

4. The method for preparing lithium phosphate from carbonate-type salt lake brine according to claim 1 or 2, characterized in that, In step (2), the non-strongly basic phosphate is one or more of disodium hydrogen phosphate, sodium dihydrogen phosphate and sodium phosphate; the addition amount of the phosphate is 50-300% of the molar amount of lithium in the lithium carbonate saturated brine.

5. The method for preparing lithium phosphate from carbonate-type salt lake brine according to claim 3, characterized in that, In step (2), the non-strongly basic phosphate is one or more of disodium hydrogen phosphate, sodium dihydrogen phosphate and sodium phosphate; the addition amount of the phosphate is 50-300% of the molar amount of lithium in the lithium carbonate saturated brine.

6. The method for preparing lithium phosphate from carbonate-type salt lake brine according to claim 1 or 2, characterized in that, In step (2), the temperature of the heating and aging is 70-100 °C, and the time of the heating and aging is 10-200 minutes.

7. The method for preparing lithium phosphate from carbonate-type salt lake brine according to claim 3, characterized in that, In step (2), the temperature of the heating and aging is 70-100 °C, and the time of the heating and aging is 10-200 minutes.

8. The method for preparing lithium phosphate from carbonated salt lake brine according to claim 4, characterized in that, In step (2), the temperature of the heating and aging is 70-100 °C, and the time of the heating and aging is 10-200 minutes.

9. The method for preparing lithium phosphate from carbonated salt lake brine according to claim 1 or 2, characterized in that, In step (3), the crude lithium phosphate contains 10-30 wt% lithium carbonate.

10. The method for preparing lithium phosphate from carbonate-type salt lake brine according to claim 1 or 2, characterized in that, In steps (3) and (4), after washing the solid, collect the mother liquor and brine of the solid-liquid separation, add 105-110% CaCl2 of the total molar amount of phosphate in the mother liquor and brine, react for 30-100 minutes, and then perform solid-liquid separation to obtain calcium hydrogen phosphate solid and brine with a phosphate content ≤ 0.005 g / L, and return the obtained brine to the lake for recycling.