Method for recovering lead from lead-containing discarded electronic waste cathode ray tube glass

Abstract

A method for recovering lead from lead-containing discarded electronic waste cathode ray tube glass includes the steps of taking a sample of cathode ray tube lead-containing funnel glass, crushing to obtain CRT glass powder, then uniformly mixing zero-valent iron powder with the CRT glass powder according to the mass ratio of 0.1-1.5:1, performing heat preservation at a temperature of 610-960 C. for 3-180 min, and further cooling to extract the metallic lead from a SiO.sub.2 reticular glass structure of the CRT glass. This can be applied to pretreatment of the lead-containing waste CRT glass, and the metallic lead is extracted from the reticular silicate structure of the lead-containing waste CRT glass by adding the zero-valent iron in the thermal treatment process so that disposal rate of electronic wastes is improved and ecological safety is ensured. This method has important environmental, social and economic significance and broad application prospects.

Claims

1. A method for recovering lead from lead-containing discarded electronic waste cathode ray tube (CRT) glass, comprising the steps of: taking a sample of cathode ray tube lead-containing funnel glass; crushing the sample to obtain CRT glass powder; preparing a mixture by mixing zero-valent iron powder with the CRT glass powder according to a mass ratio of 0.1-1.5:1; performing heat preservation of the mixture at a temperature of 610-960 C. for 3-180 min; and cooling the mixture to extract metallic lead from a SiO.sub.2 reticular glass structure of the CRT glass.

2. The method according to claim 1, wherein the step of taking includes breaking a funnel screen joint part of the CRT and taking the sample of the cathode ray tube lead-containing funnel glass from the funnel screen joint part, and wherein the step of crushing includes breaking the sample until the particle size is 1-3 cm, crushing by a planetary ball mill until the particle size is less than 65 meshes, and drying at a temperature of 105 C. for 24 h to obtain the CRT glass powder.

3. The method according to claim 1, wherein the temperature is 610-910 C.

4. The method according to claim 3, wherein the heat preservation is for 15-45 min.

5. The method according to claim 1, wherein the heat preservation is for 15-45 min.

6. The method according to claim 1, wherein the mass ratio of the zero-valent iron powder to the CRT glass powder is 1.5:1, the temperature is 710 C., and the heat preservation is for 30 min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows effects of weight ratio of zero-valent iron powder/lead-containing CRT glass power on extraction rate of metallic lead when the temperature is 710 C. and the heat preservation time is 30 min; and

(2) FIG. 2 shows effects of different thermal treatment time in the range of 3-180 min on extraction rate of metallic lead when weight ratio of zero-valent iron powder/lead-containing CRT glass power is 1/1 at three temperatures of 610 C., 710 C. and 960 C. respectively.

DETAILED DESCRIPTION OF THE INVENTION

(3) The following embodiments are used for further describing the invention rather than limiting the invention.

(4) The method for recovering lead from lead-containing discarded electronic waste cathode ray tube glass of the invention comprises the following steps:

(5) 1. Preparation of lead-containing discarded electronic waste cathode ray tube glass powder and method for mixing lead-containing discarded electronic waste cathode ray tube glass powder with zero-valent iron powder

(6) The lead-containing discarded electronic waste cathode ray tube glass is waste colored display screen funnel glass with the lead content of about 20 wt. %.

(7) (1) Break and separate the funnel screen joint part of the waste colored display screen CRT, and take the lead-containing funnel glass of the funnel part as a sample. Completely remove surface coating on the lead-containing funnel part glass by a wet washing method.

(8) (2) Break the lead-containing funnel glass after removal of the surface coating, grind till the particle size is about 1-3 cm, and then perform further crushing by a planetary ball mill.

(9) (3) Sieve the powder after crushing by a 65-mesh sieve, place the sieved powder (<65 meshes) into an oven at the temperature of 105 C., and dry for 24 h to obtain the CRT glass powder for later use.

(10) (4) The purity of zero-valent iron powder which is used as a reducing agent is more than 99%, and the particle size is less than 80 meshes. The zero-valent iron powder is firstly in a sealed state and can be used immediately after being taken.

(11) (5) Weigh the zero-valent iron powder and the CRT glass powder according to the mass ratio of 0.1-1.5:1 and perform ball milling for uniform mixing.

(12) (6) Press the powder after mixing into cylindrical cakes with the diameter of 20 mm and the thickness of 5 mm at room temperature and the pressure of 650 MPa to ensure the close binding of the powder in the heating process and be conductive to thermal treatment reaction.

(13) 2. Input type thermal treatment of mixture of lead-containing CRT glass powder and zero-valent iron powder

(14) (1) Firstly place the compacted cylindrical cakes in the oven at the temperature of 105 C. for later use, and weigh and record each cylindrical cake which needs to be subjected to thermal treatment.

(15) (2) Simultaneously place a corundum crucible in the oven at the temperature of 105 C. for later use. Place the weighed cylindrical cakes in the corundum crucible. and weigh again.

(16) (3) Heat a muffle furnace to 610-960 C., preferably 610-910 C., stabilize, then put the corundum crucible containing the cylindrical cakes into the muffle furnace, and perform thermal treatment reaction for 3-180 min, preferably 15-45 min.

(17) (4) When the reaction time is up to the target time, immediately take out the crucible with heat insulation gloves in conjunction with fireproof pliers, place in air, and naturally cool to room temperature.

(18) (5) Weigh and record the weight of each of the cooled cylindrical cakes and the corundum crucible.

(19) (6) Break the corundum crucible, take out the cylindrical cakes, grind into powder, and perform X-ray and X-ray fluorescence (XRF) analysis to analyze the lead extraction efficiency.

(20) The metallic lead in the cylindrical cakes can be purified to obtain the elemental metallic lead by flotation, chemical extraction or other conventional ore dressing methods.

(21) Embodiment 1: Effects of thermal treatment temperature on lead extraction efficiency

(22) The operation is performed by referring to the steps of the above method for recovering the lead from the lead-containing discarded electronic waste cathode ray tube glass, some parameters therein are changed or embodied but others are the same, and the specific steps are as follows:

(23) Mix zero-valent iron powder and lead-containing CRT glass powder according to the mass ratio of 0.1:1 and 1.5:1, press into cylindrical cakes, and heat at the temperature of 500-960 C. (see Table 1) for 30 min. It can be seen from an X-ray diffraction spectrum that when the thermal treatment temperature is lower than 610 C., iron does not interact with the lead-containing glass, and only the iron is oxidized by oxygen in air. At the temperature of 610 C., the formation of a metallic lead phase is firstly observed. In addition, as the temperature rises, the signal of the metallic lead phase is significantly increased. At the temperature of 710 C., the highest formation rate of crystal lead is obtained, the thermal reduction reaction for extracting the lead from a lead-containing glass body by taking zero-valent iron as a reducing agent can be realized, and the described crystallization process is as shown in formula (1):
SiOPb++Fe(0).fwdarw.Pb(0)+Fe+OSi(1)

(24) As the temperature rises further, the signal strength of the metallic lead phase is not increased. Such phenomenon seems to indicate that the sharp drop in the signal strength of the metallic lead phase is caused by volatilization of the metallic lead and/or vitrification of the lead due to returning of the extracted metallic lead into a glass matrix.

(25) TABLE-US-00001 TABLE 1 Effects of thermal treatment temperature on formation of metallic lead phase Formation rate of metallic lead phase % Thermal The mass ratio of zero- The mass ratio of treatment valent iron/lead- zero-valent iron/ temperature containing CRT glass lead-containing CRT ( C.) powder is 0.1:1 glass powder is 1.5:1 500 0 0 610 4.20 11.74 660 19.66 33.40 710 34.78 50.67 760 28.58 45.08 810 25.80 36.73 860 16.04 23.50 910 5.38 11.92 960 0 8.88
Embodiment 2: Determination of possibility of lead evaporation in experimental process

(26) The operation is performed by referring to the steps of the above method for recovering the lead from the lead-containing discarded electronic waste cathode ray tube glass, some parameters therein are changed or embodied but others are the same, and the specific steps are as follows:

(27) In order to eliminate the possibility of lead evaporation in the experimental process, weight a sample in which the mass ratio of zero-valent iron powder to lead-containing CRT glass powder is 0.1:1, mix, press into cylindrical cakes, and further perform thermal treatment in the temperature range of 600-960 C. (see Table 2). Weigh the sample after thermal treatment, and perform X-ray fluorescence (XRF) inspection, wherein the weight and XRF data before and after the reaction of the sample are listed in Table 2. Calculate the loss of the lead by utilizing the weight and XRF data of the sample, wherein the lead loss at any temperature is less than 1 wt. %. The results show that the lead content in the initial sample is consistent with that in the sample after the corresponding thermal treatment. Thus, these findings confirm that no lead volatilization exists in the thermal treatment process. The comprehensive results in Embodiment 2 show that the crystal metallic lead extracted from the glass structure in the thermal treatment process can re-enter the glass matrix as the temperature rises. This embodiment indicates that the thermal treatment process has no lead volatilization effect and can not cause atmospheric pollution.

(28) TABLE-US-00002 TABLE 2 XRF results of sample at different temperatures and calculation of lead loss Thermal Lead treatment XRF results (wt. %) Weight (g) loss temperature ( C.) PbO Fe.sub.2O.sub.3 Initial Residual (%) 600 20.69 13.24 3.47 3.48 ND.sup.a 650 19.76 13.67 4.21 4.33 ND.sup.a 700 19.31 12.25 3.98 4.15 0.38 750 19.26 12.56 4.31 4.62 ND.sup.a 800 18.72 13.13 3.68 4.07 ND.sup.a 850 18.97 13.79 4.23 4.47 0.78 900 19.86 13.84 3.69 3.84 ND.sup.a 960 19.66 13.44 3.87 4.04 ND.sup.a Original CRT 20.23 12.11 ~ ~ ~ .sup.aND: Not detected
Embodiment 3: Effects of adding amount of zero-valent iron powder on lead extraction efficiency

(29) The operation is performed by referring to the steps of the above method for recovering the lead from the lead-containing discarded electronic waste cathode ray tube glass, some parameters therein are changed or embodied but others are the same, and the specific steps are as follows:

(30) In order to optimize the process parameters, investigate the effects of the adding amount of the zero-valent iron powder on the lead extraction efficiency under the conditions that the temperature is 610 C., 710 C. and 960 C. respectively and the thermal treatment time is 30 min. The results are as shown in FIG. 1, the lead content is quantitatively analyzed by X-rays, and the lead extraction rate is effectively increased along with the increase of the zero-valent iron content in the sample. In addition, when the metallic lead is reduced under the condition that the mass ratio of zero-valent iron powder/lead-containing CRT glass powder is 1/1, the extraction rate of the metallic lead is the maximum. At the temperature of 610 C., when the mass ratio of zero-valent iron powder/lead-containing CRT glass powder is increased from 0.1/1 to 0.75/1, the lead recovery ratio is increased from 4% to 20%, and when the mass ratio of zero-valent iron powder/lead-containing CRT glass powder is in the range of 0.75/1-1.5/1, the lead extraction efficiency is relatively stable and consistent. At the temperature of 960 C., the results are similar, when the mass ratio of zero-valent iron powder/lead-containing CRT glass powder is increased from 0.1/1 to 0.75/1, the lead recovery ratio is increased from 0% to 11%, however, as the mass ratio of zero-valent iron powder/lead-containing CRT glass powder is further continuously increased, the lead extraction efficiency does not change correspondingly. At the temperature of 710 C., when the mass ratio of zero-valent iron powder/lead-containing CRT glass powder is increased from 0.1/1 to 1/1, the lead extraction rate is increased as the mass ratio of zero-valent iron powder/lead-containing CRT glass powder is increased, even if the mass ratio of zero-valent iron powder/lead-containing CRT glass powder is increased to 1.5/1, the highest lead extraction rate is stabilized at about 60%, and in the recovery process, when the mass ratio of zero-valent iron powder/lead-containing CRT glass powder is increased from 1/1 to 1.5/1, the lead extraction rate is only upgraded from 58% to 60%. Thus, in view of economics, it is recommended that the lead is extracted under the condition that the mass ratio of zero-valent iron powder/lead-containing CRT glass powder is 1/1.

(31) Embodiment 4: Effects of thermal treatment time on lead extraction efficiency

(32) The operation is performed by referring to the steps of the above method for recovering the lead from the lead-containing discarded electronic waste cathode ray tube glass, some parameters therein are changed or embodied but others are the same, and the specific steps are as follows:

(33) In this embodiment, investigate the effects of thermal treatment time on the lead extraction efficiency. Prepare a mixture in which the mass ratio of zero-valent iron powder/lead-containing CRT glass powder is 1/1 into cylindrical cakes, and perform thermal treatment respectively at three temperatures of 610 C., 710 C. and 960 C. for different periods of time in the range of 3-180 min, wherein the results are as shown in Table 2. At the temperature of 610 C., through the thermal treatment effect in a long period of time of 180 min, the extraction rate of the metallic lead is increased to 35%. When the temperature is 710 C., from 3 min to 30 min, the lead extraction rate is directly proportional to the thermal treatment time, and when the thermal treatment holding time is increased from 30 min to 180 min, the lead extraction rate is reduced to 35%. When the thermal treatment temperature is 960 C., the lead extraction efficiency is inversely proportional to the thermal treatment holding time, the extraction rate of crystal lead rapidly reaches 25% within 3 min, and the extraction efficiency is reduced as the thermal treatment time is prolonged.

(34) The results of this embodiment indicate that in the thermal treatment process, there are two mechanisms, namely lead extraction reaction as described in formula (1) and reaction for vitrifying the extracted metallic lead into the glass matrix, as shown in formula (2):
SiOSi+Pb(0).fwdarw.SiOPb++Si(2)

(35) The higher temperature and the longer thermal treatment time can further melt the glass, thereby vitrifying the metallic lead into the glass matrix and having great negative effects on extraction of the lead from the glass structure. The optimal experimental conditions are as follows: the mass ratio of zero-valent iron powder/lead-containing CRT glass powder is 1.5/1, the temperature is 710 C., and the thermal treatment is performed for 30 min.

(36) The above descriptions are only preferable embodiments of the invention and not intended to limit the invention. Any modifications, equivalent substitutions, improvements and the like made within the spirit and the principle of the invention should fall within the protection scope of the invention.