Patent Application
20130129585
The present application claims priority to Chinese Application No. 201010249152.7, entitled Method for Treating Waste Glass Containing Lead, filed on Aug. 9, 2010, the entire contents of which are hereby incorporated by reference.
The present invention relates to method for treating industrial waste, more particularly, relates to a method for treating waste glass containing lead.
Glass containing lead refers to glass containing glass-formers like SiO2 and high level of PbO, which is often used for manufacturing products as optical glass, electric vacuum glass, low-temperature sealing glass, anti-radiation glass, glass beads with high refractive index and art container glass, etc.
As an important product of glass containing lead, cathode ray tube (CRT) is widely used in televisions, computer monitors, oscilloscope and other electronic equipments. Glass of CRT monitor contains a lot of PbO as well as a variety of harmful chemical ingredients, such as: 53.05% SiO2, 18.27% PbO, 3.47% Al2O3, 2.35% CaO, 1.9% BaO and 0.97% MgO (by mass fraction). Especially the glass of the funnel contains lead up to 20% to 40%. If discarded directly, it may not only cause a waste of lead resources, but also produce huge pollution to the surrounding environment, even serious harm to human health.
Because CRT displays produced in early days have reached or are about to reach the service life, and electronic technology products update at a fast speed, more and more CRT displays are (will be) obsolete and become e-waste. According to a statistics in 2008, the number of obsolete televisions and computers in China was over 500 million each year, and increased at the rate of 25 to 30% year by year. Thus, how to treat waste glass containing lead has become a hot issue of concern.
In recent years, it has been reported that sintered glass ceramics can be obtained after mixing glass containing lead and some industrial wastes followed by grinding into powders and sintering, but in this way, it is just to transfer metal lead in the glass from one product to another product, the problem of hazard of heavy metals has not been solved.
In 2008, Wu Guoqing, et al, reported a research entitled “study on technique for recycling and treating displays containing CRT” from the perspective of material classification, harmless disposal of material, material separation and recycle. That same year, Yin Fengfu, et al, at the Haier Group's technology research and development center reported a research entitled “environmental processing technology of waste displays”, as well as its partner Qingdao Xintiandi developed CRT comprehensive utilization technology, built relevant disposal and recycling factories, but their technical core is limited to CRT dismantling and classification, and does not involve in industrial production methods of extracting lead from CRT for reuse.
A Chinese patent having publication No. CN 101613802A provided a process and corresponding equipments for recycling waste glass containing lead while producing environmental building material, which takes waste glass containing lead as raw material, recycling lead therein by vacuum carbothermic reduction process and preparing foam glass. However, the process has fewer steps so it can only recycle lead and corresponding chemical product at the same time, and the process should be carried out at 1000° C. for several hours which not only requires high demands for equipments but also causes large scale energy consumption and pollution, so it is not suitable for industrial production.
Solving the above problems, the present invention aims to provide a method for treating waste glass containing lead, which can not only reduce or eliminate harmful effects of lead on environment, but also turn waste into treasure, by effectively using metal lead in waste to obtain good economic benefit, and it is reasonable and feasible, of less pollution, and can be industrialized.
The present invention provides a method for treating waste glass containing lead, comprising:
(1) providing glass containing lead, mechanically crushing, ball milling and sieving to obtain glass containing lead powders;
(2) roasting glass containing lead powders with alkaline liquor to obtain a roasted material;
(3) providing polycarboxylic acid complexing agent and nitric acid, mixing to produce leaching agent, immersing the roasted material in the leaching agent to obtain leachate;
(4) regulating pH value of the leachate, precipitating metal ion to obtain precipitates, separating and removing impurities, rinsing and drying to obtain chemical product containing lead.
Herein, the glass containing lead has a formula of RmOn-PbO—SiO2(B2O3). In the formula, SiO2(B2O3), i.e. silica(diboron trioxide), is network former which is a basic unit of the network structure of glass. RmOn, represents metallic compounds of alkali, metallic compounds of alkaline earth metal, or metallic compounds of rare-earth metal, is modifier that alters the network structure to obtain an adjusted property. PbO, i.e. lead oxide, is the characteristic constituent giving glass basic properties. With the increasing amount of PbO, the values of performance indexes of glass, such as density, refractive index, dispersion, dielectric constant, X-ray absorption coefficient and γ-ray absorption coefficient increase, but its rigidity, viscosity at high temperature, softening temperature and chemical stability decrease; resulting in more slowly changing of viscosity with temperature, colorants of bright-colored, increase of surface brightness, and crisp sounds.
Preferably, glass containing lead is glass of CRT (cathode-ray tube) displays, whose face mainly made from a series of SiO2—BaO—SrO—ZrO2—R2O—RO glass, funnel and neck mainly made from a series of SiO2—Al2O3—PbO—R2O—RO glass. R2O and RO are metallic oxides, where R can be Mg, Ca, Na or other metals elements.
Step (1) of the present invention is a pretreatment with material: providing glass containing lead as raw material, mechanically preliminarily crushing glass containing lead, then further crushing glass containing lead with ball-milling machine, collecting glass containing lead powders and sieving for later use. Preferably, the glass containing lead is preliminarily crushed into particle size of 1 to 5 cm, then followed by further crushing and passing through a 50˜100 mesh sieve. More preferably, the glass containing lead is preliminarily crushed into particle size of 1 to 3 cm, then followed by further crushing and passing through an 80˜100 mesh sieve.
Roasting with alkaline liquor of step (2) refers to steps of harmonizing glass containing lead powders obtained from step (1) with alkaline liquor to obtain paste, roasting the paste to obtain a roasted material. These steps are carried out for breaking the network structure of glass, and setting PbO wrapped in the network structure free.
Preferably, alkaline liquor used in the step of roasting with alkaline liquor is strongly alkaline liquor. Sodium carbonate and sodium nitrate are also available, but they cannot offer better results compared to strongly alkaline liquor. More preferably, said strongly alkaline liquor is NaOH. Preferably, glass containing lead powders used in the step of roasting with alkaline liquor, is mixed with alkaline liquor according to mass ratio of glass containing lead powders to solid NaOH 1:1, and harmonizing to be paste.
The chemical equation for the roasting reaction can be denoted as: SiO2+2NaOH→Na2SiO3+H2O
Preferably, the roasting temperature is in the range of 500° C. to 700° C. Preferably, the roasting time is in the range of 30 min to 5 h. More preferably, roasting temperature is 600° C. More preferably, roasting time is 3 h. What is also preferred is that step (2) further comprises grinding the roasted material and passing through an 80 mesh sieve.
Immersing of step (3) mainly refers to process of dissolving PbO wrapped in the network structure of glass in a proper leaching agent, which comprises steps of providing polycarboxylic acid complexing agent and nitric acid, mixing to produce leaching agent, immersing the roasted material obtained from step (2) in the leaching agent to obtain leachate.
The leaching agent is selected depending on capacity for complexing of polycarboxylic acid complexing agent and strong acidity of nitric acid. For the complexation reaction, equilibrium constant is expressed as stability constant of complexes (also known as formation constant of complexes), a greater value of the constant indicates a more stable complex can be formed. As used in the present invention, the term “polycarboxylic acid complexing agent” refers to carboxylic acids which have capacity for complexing, commonly have capacity for complexing with Pb2+. Both acetic acid and edetic acid (EDTA) having greater stability constant of complex (with Pb2+) are preferred in the present invention. These two polycarboxylic acid complexing agents have strong capacity for complexing, thus can form stable complexes with metal lead. Polycarboxylic acid complex can also be selected from glycine, methanoic acid, glycolic acid, pyruvic acid, lactic acid, malic acid and others, but their capacities for complexing are not good enough.
Preferably, polycarboxylic acid complexing agent is acetic acid, which mixed with nitric acid according to the volume ratio of 3:1 to 9. More preferably, acetic acid is mixed with nitric acid according to the volume ratio of 1:1. Preferably, the concentration of acetic acid is 17 mol/L, the concentration of nitric acid is 15 mol/L.
Step of immersing the roasted material can comprise providing the roasted material and adding water, then placing into leaching agent and immersing. Alternatively, step of immersing the roasted material can comprise placing the roasted material into diluted leaching agent and immersing.
Preferably, placing the roasted material obtained from step (2) into water according to the solid-liquid ratio of roasted material to water ranged from 1:4 to 6, and adding leaching agent according to the solid-liquid ratio of roasted material to nitric acid in the range of 1:1 to 4, and immersing.
More preferably, placing the roasted material obtained from step (2) into water according to the solid-liquid ratio of roasted material to water 1:5, and adding leaching agent according to the solid-liquid ratio of roasted material to nitric acid 1:3, and immersing, herein, volume ratio of acetic acid to nitric acid in leaching agent is 1:1, at the same time, providing 1 portion of roasted material, adding 5 portions of water, 3 portions of acetic acid and 3 portions of nitric acid, mixing and immersing; Alternatively, providing 3 portions of acetic acid, 3 portions of nitric acid and 5 portions of water, mixing to obtain diluted leaching agent, then placing 1 portion of roasted material into the leaching agent and immersing.
The chemical equations for immersing reaction can be denoted as:
Na2SiO3+2HNO3→H2SiO3+2NaNO3
2PbO+2HAc→Pb(OH)2.Pb(Ac)2
PbO+2HNO3→Pb(NO3)2+H2O
Step of immersing is carried out for lead to be immersed into leachate: lead that has not yet been set free is set free by complexing little by little due to a strong complexing interaction of acetate ion with lead.
Preferably, immersing temperature is in the range of 60° C. to 100° C. Preferably, immersing time is in the range of 1 to 5 h. More preferably, immersing temperature is 90° C. More preferably, immersing time is 4 h. What is also preferred is that step (3) further comprises filtrating leachate and rinsing.
Step (4) comprises: regulating pH value of leachate; precipitating Pb, Ba and other metal ions in leachate in one step or stepwise to obtain precipitates; separating and removing impurities, rinsing and drying to obtain chemical product containing lead.
Preferably, after said precipitates formed from metal ions are obtained, step (4) further comprises steps of transforming precipitates, and then separating and removing impurities.
More preferably, step (4) comprises: adding strongly alkaline liquor into leachate, regulating pH value of the leachate to 1˜3; adding SO42− into leachate, precipitating Pb2+ and Ba2+ to obtain PbSO4 and BaSO4 precipitates; adding CO32−, transforming PbSO4 precipitate into PbCO3, adding HNO3 solution, reacting to obtain Pb(NO3)2; filtrating, separating solid (BaSO4) and liquid (Pb(NO3)2), removing impurities; taking filtrate liquid and adding SO42− to precipitate Pb2+ to obtain PbSO4; at last, adding strongly alkaline liquor to regulate pH value to 8˜10, rinsing, drying to obtain product PbO.PbSO4.H2O (tribasic lead sulfate).
The chemical equations can be denoted as:
the first precipitation: Pb2++SO42−→PbSO4
Ba2++SO42−→BaSO4
transformation of precipitates: PbSO4+CO32−→PbCO3+SO42−
dissolving of precipitates: PbCO3+2HNO3→Pb(NO3)2+H2O+CO2
the second precipitation: Pb2++SO42−→PbSO4
synthesis of product: 4PbSO4+6OH−→3PbO.PbSO4.H2O+3SO42−+2H2O
And more preferably, step (4) comprises: adding 20% sodium hydroxide solution into leachate, regulating pH value of the leachate to 1; adding SO42− into leachate according to the ratio of n(SO42−):n(Pb2+)=1.2˜1.5:1, precipitating Pb2+ and Ba2+ to obtain PbSO4 and BaSO4 precipitates; adding CO32− according to the ratio of n(CO32−):n(Pb2+)=2˜2.5:1, transforming PbSO4 precipitate into PbCO3, adding HNO3 solution, reacting to obtain Pb(NO3)2; filtrating, separating solid (BaSO4) and liquid (Pb(NO3)2), removing impurities; proving filtrate liquid and adding SO42− according to the ratio of n(SO42−):n(Pb2+)=1.2˜1.5:1 to precipitate Pb2+ to obtain highly purified PbSO4; at last, adding 20% NaOH solution to regulate pH value to 9, rinsing, drying to obtain product PbO.PbSO4.H2O (tribasic lead sulfate).
Alternatively, step (4) preferably further comprises: regulating the pH value of leachate to 11˜12; precipitating Pb2+ to obtain Pb(OH)2 precipitate; filtrating, separating solid and liquid, removing impurities; taking solid dregs, adding HNO3 solution to regulate pH value to 0.5˜1, reacting to obtain Pb(NO3)2; adding SO42− to precipitate Pb2+ to obtain PbSO4; at last, adding strongly alkaline liquor to regulate pH value to 8˜10, rinsing, drying to obtain product PbO.PbSO4.H2O (tribasic lead sulfate). Herein, leachate may contain Al3+, Mg2+ and Ca2+ metal ions, which are precipitated to form Al(OH)3, Mg(OH)2 and Ca(OH)2 precipitates at pH 11˜12. When solid and liquid are separated, the purpose of separating the above precipitates and Ba2+ is achieved.
The chemical equations can be denoted as:
the first precipitation: Mn++nOH−→M(OH)n (M stands for Pb, may contain Al, Mg and Ca)
dissolving of precipitates: M(OH)n+nHNO3→M(NO3)n+nH2O
the second precipitation: Pb2++SO42−→PbSO4
synthesis of product: 4PbSO4+6OH−→3PbO.PbSO4.H2O+3SO42−+2H2O
More preferably, step (4) comprises: adding NaOH to regulate pH value to 12; precipitating Pb2+ to obtain Pb(OH)2 precipitate; filtrating, separating solid and liquid, removing impurities; taking solid dregs, adding HNO3 solution to regulate pH value to 1, reacting to obtain Pb(NO3)2; adding SO42− according to the ratio of n(SO42):n(Pb2+)=1.5˜2:1 to precipitate Pb2+ to obtain PbSO4; at last, adding 20% NaOH solution to regulate pH value to 9, rinsing, drying to obtain product PbO.PbSO4.H2O (tribasic lead sulfate).
Herein, step of adding NaOH to regulate pH value to 12 is preferably carried out as follows: adding solid NaOH to regulate pH value to 6, then adding 10 mol/L NaOH solution to regulate pH value to 12 so as to avoid inaccurate regulation that may occur when solid NaOH is directly used to regulate the pH value at terminal point.
Chemical product containing Pb obtained in the present invention, PbO.PbSO4.H2O, can be widely used in manufacturing heat stabilizer, wire and cable, and the process is of good matching, have high economic value in use.
The method for recycling lead from waste glass containing lead provided in the present invention has the following beneficial effects.
(1) Treating waste CRT reasonably, so as to reduce or eliminate harmful effects of lead on environment.
(2) Turning waste into treasure, effectively using metal lead in waste to produce chemical product containing lead of wide range of uses, good economic benefit, using lead-free dross to produce other useful functional material.
(3) Reasonable and feasible, less pollution, being industrialized.
The following description will depict preferred embodiments of the present invention in more detail. It should be noted that, those skilled in the art will recognize that the invention can be practiced with modification within the spirit of the principle, and the modification is also within the scope of protection of the present invention.
As shown in
(1) providing glass containing lead, mechanically crushing, ball milling and sieving to obtain glass containing lead powders;
providing funnel glass of CRT as raw material, mechanically preliminarily crushing glass containing lead into particle size of 1 cm, then further crushing funnel glass of CRT with ball milling machine, collecting funnel glass powders of CRT and passing through an 80 mesh sieve for later use;
Components of funnel glass of CRT are tested, the results are shown in Table. 1:
(2) roasting glass containing lead powders with alkaline liquor to obtain a roasted material
Providing solid NaOH and mixing with funnel glass of CRT according to mass ratio of 1:1, harmonizing with water to obtain paste; roasting the paste at 500° C. for 3 h to obtain a roasted material. These steps are carried out for breaking the network structure of glass, and setting PbO wrapped in the network structure free.
(3) providing acetic acid and nitric acid, mixing to produce leaching agent, immersing the roasted material in the leaching agent to obtain leachate
Providing 75 mL of acetic acid (17 mol/L) and 150 mL of nitric acid (15 mol/L), and mixing well to produce leaching agent. Taking 50 g of funnel glass of CRT roasted material, adding 250 mL of water, then placing into leaching agent, immersing at 60° C. for 4 h to obtain leachate. The step of immersing is carried out for dissolving PbO into leaching agent.
(4) regulating pH value of the leachate, precipitating metal ion to obtain precipitates, transforming precipitates, separating and removing impurities, rinsing and drying to obtain chemical product containing lead
adding 20% sodium hydroxide solution into leachate, regulating pH value of the leachate to 1; adding K2SO4 into leachate according to the ratio of n(SO42−):n(Pb2+)=1.2, precipitating Pb2+ and Ba2+ to obtain PbSO4 and BaSO4 precipitates; adding 140 g/L of Na2CO3 solution according to the ratio of n(CO32−):n(Pb2+)=2:1, converting PbSO4 precipitate into PbCO3, adding HNO3 solution, regulating pH value to 0.5, reacting to obtain Pb(NO3)2 with a fairly small amount of impurities; filtrating, separating solid (BaSO4) and liquid (Pb(NO3)2), removing impurities; taking filtrate liquid and adding Na2SO4 according to the ratio of n(SO42−):n(Pb2+)=1.2:1 to precipitate Pb2+ to obtain highly purified PbSO4; at last, adding 20% NaOH solution to regulate pH value to 9, rinsing, drying to obtain product PbO.PbSO4.H2O (tribasic lead sulfate).
As shown in
(1) providing funnel glass of CRT as raw material, preliminarily mechanically crushing glass containing lead into particle size of 3 cm, then further crushing funnel glass of CRT with ball milling machine, collecting funnel glass powders of CRT and passing through a 100 mesh sieve for later use;
(2) roasting glass containing lead powders with alkaline liquor to obtain a roasted material
Providing solid NaOH and mixing with funnel glass of CRT according to mass ratio of 1:1, harmonizing with water to obtain paste; roasting the paste at 600° C. for 13 h to obtain a roasted material. Grinding the roasted material and passing through an 80 mesh sieve
These steps are carried out for breaking the network structure of glass, and setting PbO wrapped in the network structure free.
(3) providing acetic acid and nitric acid, mixing to produce leaching agent, immersing the roasted material in the leaching agent to obtain leachate
Providing 60 mL of acetic acid (17 mol/L) and 60 mL of nitric acid (15 mol/L), and mixing well to produce leaching agent. Taking 20 g of funnel glass of CRT roasted material, adding 100 mL of water, then placing into leaching agent, immersing at 80° C. for 3 h to obtain leachate. The step of immersing is carried out for dissolving PbO into leaching agent.
(4) regulating pH value of the leachate, precipitating metal ion to obtain precipitates, transforming precipitates, separating and removing impurities, rinsing and drying to obtain chemical product containing lead
Adding solid NaOH to regulate pH value of leachate to 6, then adding 10 mol/L NaOH solution to regulate pH value to 12; precipitating Pb2+ to obtain Pb(OH)2 precipitate; filtrating, separating solid and liquid, removing impurities; taking solid dregs, adding HNO3 solution to regulate pH value to 1, reacting to obtain Pb(NO3)2; adding Na2SO4 according to the ratio of n(SO42−):n(Pb2+)=1.5:1 to precipitate Pb2+ to obtain PbSO4; at last, adding 20% NaOH solution to regulate pH value to 9, rinsing, drying to obtain product PbO.PbSO4.H2O (tribasic lead sulfate).
Method 1
For details about specific steps, see Example 1.
The step of immersing refers to process of dissolving PbO wrapped in the network structure of glass in a proper leaching agent. In the present experiment, glass is previously roasted with alkaline liquor, then immersed out using nitric acid-acetic acid as leaching agent at a certain temperature. The results are shown in Table. 2. Leaching rate can reach more than 95%, content of lead in glass falls below 1% after being treated.
Optimal combination shown in Table. 3 comprises reaction temperature 3 (100° C.), roasting temperature 3 (700° C.), amount of HAc 3 (150 mL) and amount of HNO3 3 (150 mL).
However, when applied in practical production, the leaching rate is also very high (97.5%) under the following combination condition: reaction temperature 2 (80° C.), roasting temperature 2 (600° C.), amount of HAc 2 (100 mL) and amount of HNO3 2 (100 mL).
(2) The First Precipitation
Pb2+ and Ba2+ in solution are transformed into precipitates, and then separated. Specifically, adding sodium hydroxide into leachate, regulating pH value of leachate; adding SO42− into leachate, precipitating Pb2+ and Ba2+ to obtain PbSO4 and BaSO4 precipitates.
Precipitation rate of Pb2+ precipitated by K2SO4 at different acidities are shown in Table. 4:
Conclusions: H+ concentration has great impact on precipitation of the system, as shown in Table. 4, precipitation rate of Pb reaches 98.07% when the H+ concentration is 0.09, then declines with increasing acidity of the system; when the H+ concentration is 0.38, precipitation rate of Pb is 88.36%, below 90%. Thus, the H+ concentration of the system cannot be too large. In other words, under the premise of guaranteeing a high precipitation rate, acidity of the system must be regulated (increase the pH value to about 1) before precipitating.
(3) Transformation of Precipitates
Preparing HAc—HNO3 solution containing two types of metal ions four times as much as the amount of original filtrate liquid, concentrations of two types of original leached metals are Pb: 30 g/L and Ca: 3 g/L, then regulating pH value of solution to 1, precipitating using Na2SO4 which is in excess of 1.5 times, filtrating and rinsing, then transforming PbSO4 precipitates using 140 g/L of Na2CO3 solution, rinsing and filtrating, at last, dissolving precipitates with HNO3, fixing the pH value of solution at terminal point to be about 1, reacting for 1 h, and the test results are shown in Table. 5:
Conclusions: all transformation rates of Pb after being transformed by Na2CO3 solution of different excess coefficients are greater than 96%.
(4) Synthesis of Product
Synthesis experiment, regulating pH value at terminal point of the system to 9 by using 20% sodium hydroxide solution and results are shown in Table. 6:
Conclusions: compared to industry standards, the synthesized products meet the standard of first grade product.
Method 2
For details about specific steps, see Example 2.
See Method 1.
(2) Precipitation
Regulating pH value of original filtrate liquid to 10˜14 with NaOH, precipitation rates of kinds of metal ions are shown in Table. 7:
Conclusions: it can be seen from Table. 7 that pH values are too low, precipitation rates of Pb are low; when pH value is 12, precipitation rate of Pb increases, however, when pH value increases to 14, precipitation of Pb declines because Pb(OH)2 can dissolve in strong alkali, thus, the best pH value at terminal point for precipitation is 12.
(3) Dissolving and Precipitation
Data is the same as that of the first precipitation
(4) Synthesis of Product
Adding appropriate concentrated HNO3 into slurring wet Pb(OH)2 solution to regulate its pH value to 0.5 to 1, adding Na2SO4 which is in excess of 1.5˜2 times, precipitating to obtain PbSO4, then adding 20% sodium hydroxide to regulate pH value of slurring PbSO4 to 9 to obtain tribasic lead sulfate meeting industry standards, shown in Table. 8:
Conclusions: process flow of such method is very short, compared to industry standards, the synthesized products meet the standard of first grade product.
Comparing the above two methods, Method 1 is a favorable method for controlling the cost because consumed acid and alkaline liquor are less in the step of “precipitating metal ion to obtain precipitates, separating and removing impurities”; Method 2 is a more simple method because step of transformation of precipitates is omitted.
Chemical product containing Pb of the present invention, PbO.PbSO4.H2O, can be widely used in manufacturing heat stabilizer, wire and cable, and the process is of good matching, have high economic value in use.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201010249152.7 | Aug 2010 | CN | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CN2010/078160 | 10/27/2010 | WO | 00 | 2/5/2013 |
