METHOD FOR PREPARING GENERAL-PURPOSE CEMENT BY CHLORINATION ROASTING OF ALUMINOSILICATES

Abstract

A method for preparing a general-purpose cement by chlorination roasting of aluminosilicates is provided, in which a mixture of aluminosilicates and sodium chloride is roasted in a steam atmosphere to obtain a roasted slag. The roasted slag is mixed with a material containing calcium oxide and magnesium oxide and ground to prepare a raw meal powder. The raw meal powder is subjected to oxidative calcination at a temperature not lower than 1240 C., followed by rapid cooling to obtain a calcined slag. The calcined slag is mixed with 0-3% by weight of caustic alkali and ground to obtain the general-purpose cement.

Claims

1. A method for preparing a general-purpose cement by chlorination roasting of aluminosilicates, comprising: (1) roasting a mixture of the aluminosilicates and sodium chloride in a steam atmosphere followed by fume discharge to obtain a solid roasted slag, wherein main chemical components of the aluminosilicates are SiO.sub.2 and Al.sub.2O.sub.3; (2) quantitatively mixing the solid roasted slag with a material containing CaO and MgO followed by grinding to obtain a powder mixture, or grinding the solid roasted slag followed by washing, drying, and mixing with a powder material containing CaO and MgO to obtain a powder mixture; (3) subjecting the powder mixture to oxidative calcination at a temperature not lower than 1240 C. until a stable state with liquid phase dominated is formed, and cooling to obtain a calcined slag; and (4) mixing the calcined slag with an alkali followed by grinding to obtain the general-purpose cement in a powder form, wherein the alkali is sodium hydroxide, potassium hydroxide or a combination thereof; or grinding the calcined slag separately to obtain an active powder component of the general-purpose cement for storage, and mixing the active powder component with an aqueous solution of the alkali to produce a slurry of the general-purpose cement for use.

2. The method of claim 1, wherein in step (1), a steam flow rate is at least 60 g.Math.min.sup.1.Math.m.sup.2.

3. The method of claim 1, wherein in step (1), a maximum roasting temperature is 800-1000 C.

4. The method of claim 1, wherein in step (1), a holding time at a maximum roasting temperature is at least 1 h.

5. The method of claim 1, wherein in a slag produced from the aluminosilicates by oxidative calcination at 950 C., a total weight percentage of SiO.sub.2, Al.sub.2O.sub.3, Fe.sub.2O.sub.3, CaO, MgO, Na.sub.2O and K.sub.2O is greater than 90.0%, and a weight ratio of SiO.sub.2 to Al.sub.2O.sub.3 to Fe.sub.2O.sub.3 to CaO to MgO to a combination of Na.sub.2O and K.sub.2O is 49.0-82.5:10.0-46.0:0-8.1:0-5.0:0-9.5:0-12.2.

6. The method of claim 1, wherein the mixture of the aluminosilicates and sodium chloride in step (1) is produced through steps of: mixing the aluminosilicates with sodium chloride followed by grinding and sieving with an 80-m square-hole sieve.

7. The method of claim 1, wherein in step (1), the sodium chloride is 45.0% or less of a total weight of SiO.sub.2 and Al.sub.2O.sub.3 in the aluminosilicates.

8. The method of claim 1, wherein in the calcined slag obtained in step (3), a weight ratio of SiO.sub.2 to Al.sub.2O.sub.3 to Fe.sub.2O.sub.3 to CaO to MgO to a combination of Na.sub.2O and K.sub.2O is 30.0-42.0:10.0-17.0:0-6.0:22.0-46.0:0-16.0:3.1-8.3.

9. The method of claim 1, wherein in step (4), a mass of the alkali is calculated according to the following formula:
(NaOH+0.713KOH)/the calcined slag=0-3.0%.

10. The method of claim 1, wherein in step (1), a discharged fume is introduced into water for dissolution and collection, and a resultant aqueous solution is used to produce HCl gas or hydrochloric acid, or for recovering valuable metals.

Description

DETAILED DESCRIPTION OF EMBODIMENTS

[0031] The present disclosure will be described in detail below with reference to embodiments. It should be noted that the described embodiments are merely illustrative, and are not intended to limit the disclosure.

[0032] The embodiments are each described in three parts: chlorination roasting, raw meal calcination, and cement hydration and curing.

(1) Chlorination Roasting

[0033] The aluminosilicate samples (dominated by SiO.sub.2 and Al.sub.2O.sub.3) used herein included two kind of lead-zinc tailings, one kind of gold tailings, one kind of lithium tailings and eight kind of aluminosilicate rock mixtures. In addition to the common rock-forming element oxides, metal mine tailings also contained some valuable metals with a high recovery value. With respect to a calcined product obtained by oxidative calcination of each of the listed samples at 950 C., a total weight percentage of SiO.sub.2+Al.sub.2O.sub.3+Fe.sub.2O.sub.3+CaO+MgO+Na.sub.2O+K.sub.2O was greater than 90.0%. A weight ratio of SiO.sub.2 to Al.sub.2O.sub.3 to Fe.sub.2O.sub.3 to CaO to MgO to a combination of Na.sub.2O and K.sub.2O is 49.0-82.5:10.0-46.0:0-8.1:0-5.0:0-9.5:0-12.2. The dried aluminosilicates and sodium chloride were mixed and ground, where the sodium chloride accounted for 45.0% or less of a total weight of SiO.sub.2 and Al.sub.2O.sub.3 in the aluminosilicates. Then, the fineness of the ground mixed powder was tested using an 80-m square-hole sieve, and the mixed powder in the examples was sieved with the 80-m square-hole sieve. Then, the ground mixed powder was transferred to a boat-shaped crucible and placed in a tubular atmosphere furnace. The temperature was increased at a rate of 5 C./min. When the temperature reached 500 C., steam was introduced, and when the temperature reached 800-1000 C., it was held for 1-4 h. The power was then turned off and the steam supply was terminated, and the intake pipe was connected to air. During roasting, a discharged fume was introduced into water for dissolution and continued until the roasted slag cooled to room temperature, after which the fume discharged was stopped. During roasting, a steam flow rate was at least 60 g.Math.min.sup.1.Math.m.sup.2 and could reach up to 700 g.Math.min.sup.1.Math.m.sup.2. The process parameters for each example were detailed in Table 1.

TABLE-US-00001 TABLE 1 Process parameters for chlorination roasting of aluminosilicates with sodium chloride Chemical composition of the Maximum aluminosilicates calcined slag .sup.a NaCl/ roasting Roasting Steam Roasting Raw (%) (SiO.sub.2 + temperature time flow number materials SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO Na.sub.2O K.sub.2O Others Al.sub.2O.sub.3) ( C.) (h) rate .sup.b 1 Metal tailing 72.3 13.9 8.1 3.2 0.9 0.1 1.6 1.5 0.27 900 4 270 2 64.1 28.4 4.3 1.7 0.5 0.1 0.9 2.7 0.25 950 2 270 3 52.5 23.8 6.5 4.5 9.5 0.3 2.9 5.8 0.45 900 4 350 4 77.6 12.2 3.1 2.1 0.8 2.0 2.2 4.6 0.45 900 4 410 5 Aluminosilicates 82.5 10.0 1.1 3.6 0.9 0.3 1.6 1.8 0.45 900 4 690 6 mixed rock 70.5 11.7 6.3 5.0 4.2 0.7 1.6 2.9 0.45 1000 1 700 7 67.1 21.8 3.3 1.5 0.7 1.6 4.0 3.2 0.41 900 4 330 8 79.6 15.2 0.7 1.0 0.3 1.7 1.5 4.1 0.37 800 4 280 9 50.2 46.0 1.6 0.4 0.4 0.5 0.9 2.4 0.25 1000 2 60 10 55.7 41.8 0.6 0.3 0.4 0.6 0.6 6.3 0.19 900 4 250 11 49.0 30.8 7.0 0.2 0.8 0.6 11.6 1.0 0.33 900 4 250 12 56.3 42.8 0.2 0.2 0.1 0.1 0.4 3.6 0.39 850 3 250 .sup.a The content of each oxide was calculated based on SiO.sub.2 + Al.sub.2O.sub.3 + Fe.sub.2O.sub.3 + CaO + MgO + Na.sub.2O + K.sub.2O as 100%. .sup.b Unit: g .Math. min.sup.1 .Math. m.sup.2

[0034] When the aluminosilicates contained valuable metals and heavy metals, the chemical composition of the cooled roasted slag was analyzed. Based on the analysis results, the sodium chloride decomposition rate in each example (roasting number) was calculated to be 60-99.8%. Most of the sodium chloride was converted into Na.sub.2O, which remained in the roasted slag. The content of residual Cl.sup. in the roasted slag was 0.25-6.67%. After chlorination roasting, various valuable metals in the metal tailings were effectively removed. The discharged fume solution could be recycled through subsequent physical and chemical treatments to recover valuable metals and heavy metals. The aluminosilicates without valuable metals and heavy metals were subjected to chlorination roasting to produce HCl gas, which was introduced into water through the discharged fume pipe for dissolution. After distillation and purification, commercial HCl gas or hydrochloric acid was obtained. The effects of chlorination roasting in each example were detailed in Table 2.

TABLE-US-00002 TABLE 2 Chlorination roasting effects Decomposition Use of rate of sodium discharged Roasting Cl.sup. Na.sub.2O chloride fume number (%) (%) (%) Valuable metal content in roasted slag solution 1 0.25 10.6 99.8 PbO 0.0155%, removal rate of 96.5%; Recovery of ZnO 0.023%, removal rate of 66.4% valuable 2 0.60 11.4 99.5 PbO 0.0292%, removal rate of 87.2%; metals ZnO 0.019%, removal rate of 45.5% 3 4.09 17.4 68.0 Au 0.3 ppm, removal rate of 65.3%; Cu 0.013%, removal rate of 91.2% 4 2.70 16.9 77.3 Rb 0.021%, removal rate of 75.2%; Cs 0.095%, removal rate of 60.2% 5 1.51 16.3 84.9 Distillation 6 2.80 16.7 76.9 to obtain 7 6.67 16.4 60.6 HCl 8 3.81 15.4 60.0 9 0.36 8.9 65.0 10 0.09 8.9 94.8 11 0.35 12.0 91.1 12 0.65 15.7 88.8

(2) Raw Meal Calcination

[0035] The roasted slag obtained from each chlorination roasting example was mixed together with a raw material containing CaO and MgO and ground to obtain a powder mixture. The No. 7 roasted slag with high residual Cl.sup. content was ground into fine powder, washed with water, dried, and finally mixed evenly with other previously ground raw materials using a powder mixer. The other raw materials, excluding the roasted slag, included kaolin, analytical grade sodium carbonate, silicon dioxide (quartz powder), ferric oxide and natural dolomite powder. The chemical compositions of the raw materials were detailed in Table 3. The mixed powder was placed into a corundum crucible and transferred to a silicon carbide muffle furnace for calcination. The temperature was raised at a rate of 10 C./min. When the temperature reached 1240-1300 C., it was held for 1, 2, and 3 h, respectively. After the reaction was completed, the corundum crucible with the mixed powder was immediately removed from the muffle furnace and rapidly cooled by air blasting (air cooling) or water quenching (water cooling), so as to produce a calcined product mainly composed of a glass phase. A powder X-ray diffraction analysis revealed that varying the holding time during calcination of the same raw meal resulted in identical phase characteristics for clinker samples held for 2 h and 3 h, while samples held for 1 h showed some differences. Therefore, a holding time of 2 h at the maximum calcination temperature was adopted. The raw material formulations and the highest calcination temperature for each example were provided in Table 4. The calcined product was ground into fine powder to obtain a calcined material (clinker) powder. Chemical analysis showed that, in the calcined product, a weight ratio of SiO.sub.2 to Al.sub.2O.sub.3 to Fe.sub.2O.sub.3 to CaO to MgO to a combination of Na.sub.2O and K.sub.2O is 30.0-42.0:10.0-17.0:0-6.0:22.0-46.0:0-16.0:3.1-8.3 (as shown in Table 5).

TABLE-US-00003 TABLE 3 Chemical composition of other raw materials used in cement raw meal formulation (wt. %) SiO.sub.2 Al.sub.2O.sub.3 TFe.sub.2O.sub.3 CaO MgO Na.sub.2O K.sub.2O Others Kaolin 42.7 38.3 0.5 0.3 0.3 0.5 0.6 16.7 Dolomite 31.6 20.2 48.3 Sodium carbonate 58.5 41.5 Calcium carbonate 56.0 44.0 Quartz 99.9 0.1 Ferric oxide 99.9 0.1

TABLE-US-00004 TABLE 4 Cement raw meal formulation and calcination temperature (wt. %) Raw material proportions (wt. %) Roasting Calcination Calcination slag .sup.a Sodium Calcium Quartz Ferric temperature Cooling number (number) Kaolin carbonate carbonate powder oxide Dolomite ( C.) method 1 36.3(1) 12.0 10.0 1.7 40.0 1300 Air cooling 2 50.0(2) 10.0 40.0 1240 Air cooling 3 47(3) 12.0 1.0 40.0 1300 Water cooling 4 30.0(4) 15.0 55.0 1300 Air cooling 5 30.0(5) 16.0 3.0 10.0 1.0 40.0 1300 Air cooling 6 44.0(6) 8.0 48.0 1250 Water cooling 7 30.0(7)b 9.0 3.0 58.0 0.0 1300 Water cooling 8 38.0(8) 9.0 3.0 50.0 0.0 1260 Water cooling 9 24.6(9) 0.4 55.0 15.0 5.0 1300 Air cooling 10 32.0(10) 3.0 50.0 10.0 5.0 1300 Water cooling 11 32.0(11) 50.0 13.0 5.0 1300 Water cooling 12 32.0(12) 3.0 50.0 10.0 5.0 1300 Water cooling .sup.a The weight of the No. 7 roasted slag was calculated based on the total content of SiO.sub.2 + Al.sub.2O.sub.3 + Fe.sub.2O.sub.3 + CaO + MgO + Na.sub.2O + K.sub.2O. .sup.b The roasted slag was washed with water, dried and then used for batching.

(3) Cement Hydration and Curing

[0036] The calcined product was ground into fine powder. NaOH and/or KOH were dissolved in a minimum amount of water and then cooled to room temperature. The amount of NaOH and/or KOH added was determined based on the following formula: (NaOH+0.713 KOH)/the calcined product=0-3.0%. The alkali solution was mixed with the clinker powder and stirred for 2-5 min, with an appropriate amount of water added to reduce the slurry consistency for subsequent liquefaction during vibration. Then, the slurry was poured into a 404040 steel mold, vibrated for compaction, and placed in a standard cement curing chamber at 20 C. with a humidity of not less than 90% for 1 day. After curing was completed, the sample was demolded to obtain a cement paste sample. If the strength on the first day did not meet the demolding requirements, demolding was delayed. The specimens were then kept cured under humid conditions at room temperature until 3, 7 and 28 days, at which their unconfined compressive strength was tested. The cement paste formulation and compressive strength were detailed in Table 6. As shown in Table 6, it can be seen that the prepared clinker powder exhibited a certain self-gelling property, that was, it could solidify by simply adding water and showed relatively good compressive strength. As the alkali content increased, the strength of the cement showed an upward trend. The compressive strength of the cement paste at the 28.sup.th day reached a maximum of nearly 100 MPa.

TABLE-US-00005 TABLE 5 Content of rock-forming oxides and chlorine residual in calcined material (wt. %) Calcination number SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO Na.sub.2O K.sub.2O Cl.sup. 1 39.1 12.4 6.0 26.0 11.3 4.7 0.5 0.02 2 37.9 17.0 2.6 24.9 10.9 6.4 0.3 0.04 3 30.0 13.6 3.6 28.7 15.9 7.2 1.0 0.41 4 38.4 12.7 1.3 25.3 16.0 5.7 0.6 0.06 5 39.4 12.1 1.9 26.6 11.7 8.0 0.3 0.05 6 40.9 10.0 3.4 22.0 15.7 7.4 0.6 0.16 7 31.5 13.3 1.4 46.0 0.3 6.6 0.9 0.02 8 42.0 11.3 0.4 37.8 0.2 7.9 0.4 0.12 9 36.1 14.3 0.6 44.3 1.6 2.9 0.2 0.07 10 35.7 17 0.2 39.9 1.5 5.6 0.1 0.01 11 37.6 11.4 2.1 39.2 1.6 5.5 2.6 0.02 12 34.5 16.1 0.1 40.0 1.4 7.8 0.1 0.03 The oxide content was calculated based on the total content in SiO.sub.2 + Al.sub.2O.sub.3 + Fe.sub.2O.sub.3 + CaO + MgO + Na.sub.2O + K.sub.2O.

TABLE-US-00006 TABLE 6 Cement paste formulation and compressive strength of paste samples mass ratio to the Compressive strength clinker powder at different ages Calcination (wt. %) Liquid/solid (MPa) number NaOH KOH mass ratio 3-day 7-day 28-day 1 0 0 0.29 0 5.4 18.9 0.5 0.5 0.29 28.2 57.3 69.6 1.0 1.0 0.29 57.6 70.1 94.2 3.0 0 0.29 68.1 82.3 105.5 2 0 1.0 0.25 22.1 27.2 55.7 2.0 0 0.25 27.3 34.9 67.0 3 0 1.0 0.25 28.7 40.1 49.9 4 0 0 0.25 1.2 2.5 12.0 0 2.0 0.25 38.9 57.6 62.3 5 0 0 0.22 4.9 12.7 24.5 1.0 1.0 0.22 23.4 47.9 64.5 0 4.0 0.22 34.7 65.5 86.0 6 2.0 0 0.29 42.8 60.2 75.3 7 0 1.0 0.28 19.0 25.5 32.0 0 3.0 0.29 38.9 49.2 64.8 8 1.0 0 0.27 11.5 19.4 26.5 2.0 0 0.28 19.9 19.7 30.2 9 2.0 0 0.28 13.0 23.2 32.5 10 1.0 0 0.26 15.2 25.8 30.4 11 0.5 0 0.26 10.6 20.4 25.1 12 2.0 0 0.25 34.8 58.8 74.6