CN113233800B

CN113233800B - Application of heavy metal sludge high-temperature treatment slag charge and modified magnesium oxysulfate cement containing slag charge

Info

Publication number: CN113233800B
Application number: CN202110478579.2A
Authority: CN
Inventors: 张驰; 巴明芳; 张丹蕾; 郑哲溢; 王胜
Original assignee: Ningbo University
Current assignee: Ningbo University
Priority date: 2021-04-30
Filing date: 2021-04-30
Publication date: 2022-11-15
Anticipated expiration: 2041-04-30
Also published as: CN113233800A

Abstract

The invention discloses application of heavy metal sludge high-temperature treatment slag in modified magnesium oxysulfate cement, wherein ground powder obtained by grinding slag obtained by high-temperature treatment after mixing heavy metal sludge and construction slag soil is doped into the modified magnesium oxysulfate cement as an active mineral admixture. The modified magnesium oxysulfate cement is composed of light-burned magnesium oxide powder, magnesium sulfate heptahydrate, ground powder, water and a modifier, wherein the ground powder is used as an active mineral admixture in the preparation of the modified magnesium oxysulfate cement to equivalently replace 5-40 wt% of the light-burned magnesium oxide powder. The invention provides a new solution for high-value resource utilization of heavy metal sludge, the ground powder can obviously improve the net slurry fluidity of the modified magnesium oxysulfate cement-based material and the convenience of the modified magnesium oxysulfate cement in field construction, and the mechanical property of the modified magnesium oxysulfate cement is ensured. The modified magnesium oxysulfate cement has a consolidation effect on heavy metals such as Ni, cr, zn, cu and the like.

Description

Application of heavy metal sludge high-temperature treatment slag charge and modified magnesium oxysulfate cement containing slag charge

Technical Field

The invention relates to the technical field of resource utilization of heavy metal sludge, in particular to application of heavy metal sludge high-temperature treatment slag and modified magnesium oxysulfate cement containing the slag.

Background

As one of representatives of heavy metal sludge, the electroplating sludge is used as a final state substance generated after the wastewater treatment in the electroplating industry, and absorbs heavy metals such as copper, nickel, chromium, zinc, iron and the like in the wastewater, thereby seriously polluting the environment. Therefore, the property of the heavy metal sludge is researched, a proper resource utilization technology is searched, and the treatment pressure of heavy metal sludge landfill can be effectively relieved.

Along with the rapid development of the urbanization process of China, tens of millions of tons or even hundreds of millions of tons of construction wastes are generated every year, and the garbage dug in the land in the construction wastes has strong pollution and needs to be recycled. In recent years, a great deal of work is done at home and abroad in the aspects of comprehensive treatment, harm-to-benefit and waste-to-treasure of heavy metal sludge, so that not only is the harmless treatment technology of heavy metal sludge explored, but also relevant researches such as preparation of cement and sintered bricks by mixing and grinding the heavy metal sludge instead of a small part of clinker are further carried out. The Cement-Lock technology developed by the American gas technical research institute mixes substances such as slurry and the like with a modifier, high-temperature sintering is carried out, a melt is quenched and ground to prepare high-quality Cement, and heavy metal sludge and heavy metal in construction waste can be locked in the melt in the oxidation environment of a high-temperature smelting furnace; meanwhile, the stable solidification of the arsenic sulfide waste residues by using the heavy metal sludge is also a research hotspot of related environmental protection companies. Through detection, the composition types and the contents of oxides of slag materials of the heavy metal sludge and the building slag soil mixed with a certain proportion and subjected to high-temperature harmless treatment are very close to those of II-grade fly ash used in a large amount of building materials, and the slag materials have certain volcanic ash activity or potential volcanic ash activity, so that the heavy metal sludge and the building slag soil subjected to high-temperature harmless treatment are ground, and the slag materials are used as active mineral admixtures to be directly added into concrete after the volcanic ash activity is excited, and the method is an important way for realizing the utilization of high-valued resources of the heavy metal sludge.

Compared with common silicate cement, the magnesium oxysulfate cement has the characteristics of light weight, quick setting and the like, and has obvious advantages in the aspect of environmental protection due to lower calcination temperature. However, the magnesium oxysulfate cement has the defects of low strength, long setting time, poor water resistance and the like, and the large-scale application of the magnesium oxysulfate cement is limited. In recent research, the addition of citric acid is found to be effective in improving the mechanical properties of magnesium oxysulfate cement. On the basis, in order to effectively utilize the grinding powder subjected to high-temperature harmless treatment on the heavy metal sludge and the building residue soil in the magnesium oxysulfate cement, the influence of the grinding powder on the working performance, the mechanical performance, the durability and the like of a modified magnesium oxysulfate cement matrix is researched. Meanwhile, heavy metals in the sludge are important factors influencing the sludge treatment and utilization, and in order to ensure the environmental protection and safety of cement-based materials, the leaching amount of the heavy metals in the cement matrix doped with the grinding fine powder cannot exceed a standard specified value, so that the consolidation condition of the modified magnesium oxysulfate cement to the heavy metals in the heavy metal sludge under different mixing amounts of the grinding fine powder is also explored. The invention provides application of heavy metal sludge high-temperature treatment slag and modified magnesium oxysulfate cement containing the slag by combining various research results of people.

Disclosure of Invention

The invention aims to solve the technical problem of providing the application of heavy metal sludge high-temperature treatment slag and modified magnesium oxysulfate cement containing the slag aiming at the defects of the prior art. The invention provides a new solution for high-value resource utilization of heavy metal sludge, the mixing amount of the ground powder of 5-40 wt% can obviously improve the net slurry fluidity of the modified magnesium oxysulfate cement-based material, obviously improve the convenience of the on-site construction of the modified magnesium oxysulfate cement, and ensure the mechanical property of the modified magnesium oxysulfate cement. The modified magnesium oxysulfate cement containing the heavy metal sludge high-temperature treatment slag has a consolidation effect on heavy metals such as Ni, cr, zn and Cu, and the leaching concentrations of the four heavy metals in the modified magnesium oxysulfate cement mortar doped with 40% of grinding powder are all lower than the requirements in the related standards (GB 30760-2014), so that the relative safety can be ensured when the grinding powder is applied to a cement-based material.

The technical scheme adopted by the invention for solving the technical problems is as follows: the application of the heavy metal sludge high-temperature treatment slag in the modified magnesium oxysulfate cement is that the slag obtained by high-temperature treatment after the heavy metal sludge is mixed with the building slag is ground into fine powder, and the fine powder is used as an active mineral admixture to be added into the modified magnesium oxysulfate cement.

The inventor finds that the milling powder can obviously improve the fluidity of the net slurry of the modified magnesium oxysulfate cement-based material, and the effect of improving the fluidity is more obvious when the mixing amount of the milling powder is larger; along with the increase of the mixing amount of the grinding powder, the early mechanical property of the modified magnesium oxysulfate cement-based material is obviously reduced, while the reduction trend of the mechanical property along with the increase of the mixing amount of the grinding powder is more gradual in the 90d age, and the mechanical property is obviously reduced only when the mixing amount of the grinding powder is more than 40 percent; research also finds that the grinding powder can obviously reduce the early free shrinkage deformation value of the modified magnesium oxysulfate cement-based material, wherein the early free shrinkage deformation of the modified magnesium oxysulfate cement-based material containing 10% of the grinding powder is reduced by 57.1% compared with a sample without the grinding powder, and the shrinkage deformation starting time of the sample containing 40% of the grinding powder is delayed by 4 hours compared with the sample without the grinding powder; modified magnesium oxysulfate cement-based material sample containing 40% of ground powderThe leaching concentration of heavy metals is lower than the requirement of the relevant standard (GB 30760-2014); in the early stage of hydration, the hydration product 5Mg (OH) in the magnesium oxysulfate cement hardening system ₂ ·MgSO ₄ ·7H ₂ O (517 phase) was present only in minor amounts in the MMOS with the added grind, whereas after 28d, the 517 phase content in the MMOS with and without the added grind was less different; according to the analysis of a scanning electron microscope, the quantity of the 517 phases in the MMOS sample doped with the grinding fine powder at the early stage of hydration is obviously less than that of the sample not doped with the grinding fine powder, the quantity of the 517 phases in the two groups of samples after 28d is not greatly different, and the pore diameter of the sample doped with the grinding fine powder is observed to be larger. The BET specific surface area test results show that the addition of the milled powder increases the average pore size of the MMOS by about 31.0%.

Preferably, the mass ratio of the heavy metal sludge subjected to high-temperature treatment to the building residue soil is 1: (2.5-3.5).

Preferably, the high-temperature treatment process comprises the following steps: raising the temperature of the furnace from normal temperature to 1100 ℃, then adding the mixture of the heavy metal sludge and the building residue soil into the furnace, keeping the temperature for 6-8 h, then raising the temperature of the furnace to 1300 ℃, and finally lowering the temperature of the furnace from 1300 ℃ to the normal temperature within 24 h.

Preferably, the milled powder has a primary particle size of 30 to 70 μm.

The modified magnesium oxysulfate cement containing the heavy metal sludge high-temperature treatment slag comprises light-burned magnesium oxide powder, magnesium sulfate heptahydrate, ground powder, water and a modifier, wherein the ground powder is obtained by grinding the slag obtained by mixing the heavy metal sludge and building slag and performing high-temperature treatment, and the ground powder is used as an active mineral admixture in the preparation of the modified magnesium oxysulfate cement to equivalently replace 5-40 wt% of the light-burned magnesium oxide powder.

Preferably, the ground powder is used as an active mineral admixture in the preparation of the modified magnesium oxysulfate cement to equivalently replace 10 to 40 weight percent of light-burned magnesia powder.

Preferably, the mass ratio of the heavy metal sludge subjected to high-temperature treatment to the building residue soil is 1 (2.5-3.5).

Preferably, the milled powder has a primary particle size of 30 to 70 μm.

Preferably, the modifier is a citric acid modifier and/or a mineral modifier.

Compared with the prior art, the invention has the following advantages:

1. the invention creatively mixes heavy metal sludge and building residue soil, and then grinds slag charge obtained by high-temperature treatment to obtain grinding powder which is used as active mineral admixture to be added into modified magnesium oxysulfate cement, and the grinding powder is used as the active mineral admixture in the preparation of the modified magnesium oxysulfate cement to equivalently replace 5-40 wt% of light-burned magnesium oxide powder. The mixing amount of the ground powder of 5-40 wt% can obviously improve the net slurry fluidity of the modified magnesium oxysulfate cement-based material, obviously improve the convenience of the on-site construction of the modified magnesium oxysulfate cement and ensure the mechanical property of the modified magnesium oxysulfate cement. The invention provides a new solution for high-value resource utilization of heavy metal sludge.

2. The early plastic shrinkage value of the modified magnesium oxysulfate cement concrete can be obviously reduced by adding the ground powder, and the plastic shrinkage value can be reduced by over 50 percent when 10 percent of the ground powder is added. Meanwhile, with the increase of the mixing amount of the grinding powder, the initial shrinkage time of the modified magnesium oxysulfate cement concrete is delayed, and the influence of the mixing amount of the grinding powder on the total early plastic shrinkage value of the modified magnesium oxysulfate cement concrete is small.

3. The modified magnesium oxysulfate cement containing the heavy metal sludge high-temperature treatment slag material has a consolidation effect on heavy metals such as Ni, cr, zn and Cu, and the leaching concentrations of the four heavy metals in the modified magnesium oxysulfate cement mortar doped with 40% of the grinding powder are lower than the requirements in the related standards (GB 30760-2014), so that the relative safety can be ensured when the grinding powder is applied to a cement-based material.

4. After analysis through XRD, IR, TG, SEM and the like, the grinding fine powder is wrapped outside magnesium oxide particles after being doped into the modified magnesium oxysulfate cement, the hydration process of the magnesium oxysulfate cement is blocked, and the formation of 517 phase is further reduced and delayed. Meanwhile, the hole structure of the MMOS can be obviously changed by adding the grinding powder, so that the proportion of the hole diameter of 1-10 nm is obviously reduced, and the proportion of the hole diameter of more than 35nm is increased.

Drawings

FIG. 1 is a XRD analysis result of the milled powder in each example and comparative example;

FIG. 2 is SEM scanning results of the milled powder in each example and comparative example;

FIG. 3 is the XRD analysis result of the light-burned magnesium oxide powder in each example and comparative example;

FIG. 4 is a graph showing a distribution of particle diameters of a soft-burned magnesia powder and a ground powder in each of examples and comparative examples;

FIG. 5 is a graph showing the fluidity of cement paste at different amounts of grinding powder;

FIG. 6a is the compressive strength of MMOS at different amounts of milled powder and different ages, and FIG. 6b is the flexural strength of MMOS at different amounts of milled powder and different ages;

FIG. 7 shows the results of early free shrinkage deformation tests of concrete samples with different amounts of ground powder;

FIG. 8 is a diagram showing the state of a test piece of volume stability after boiling 3 hours, in which the amounts of the milled powder are 0%, 10% and 40%, respectively;

FIG. 9 shows the concentration of heavy metals in different samples;

FIG. 10a is an EDS plot of a 28 d-aged MMOS test piece doped with 40% grind, and FIG. 10b is the EDS spectroscopy analysis of the location indicated by the small box in FIG. 10;

FIG. 11 is an absorption/desorption curve obtained by nitrogen adsorption (BET) of MMOS test pieces with 0 and 30% of the content of the milled powder;

FIG. 12 is a MMOS pore size distribution for different amounts of grind;

FIGS. 13a, 13b and 13c are XRD analysis result graphs of modified magnesium oxysulfate cement test pieces in age stages of 12h, 7d and 56d, wherein the solid waste powder doping amounts are 0 and 30 percent respectively;

FIG. 14 shows the IR analysis results of modified magnesium oxysulfate cements at 14d and 28d ages with different amounts of grinding powders;

FIG. 15a and FIG. 15b are TG-DTG analysis results of modified magnesium oxysulfate cement at

age

14d and 28d, respectively;

FIGS. 16a, 16b, 16c and 16d are SEM analysis results of samples with different amounts of milled

powder

14d and 28 d.

Detailed Description

The invention is described in further detail below with reference to the accompanying examples.

Mixing heavy metal sludge and building residue soil according to the mass ratio of 1:3, and then carrying out high-temperature treatment in a kiln, wherein the high-temperature treatment process comprises the following steps: heating the furnace temperature from normal temperature to 1100 ℃, adding the mixture of heavy metal sludge and building slag soil into the furnace, keeping the temperature for 7h, heating the furnace temperature to 1300 ℃, finally cooling the furnace from 1300 ℃ to normal temperature within 24h to obtain slag, grinding the slag by a ball mill to obtain ceramsite grinding powder (grinding powder for short, GP), wherein XRD analysis results and SEM scanning results of the grinding powder are respectively shown in figures 1 and 2. The chemical composition of the milled powder of figure 1 is believed to be potentially pozzolanic.

Eight groups of MMOS mortar are prepared from the modified magnesium oxysulfate cement mixed with different mixing amounts of grinding powder according to the basic mixing ratio in the table 1 for testing, wherein the water-cement ratio of each group is 0.5, and the grinding powder is respectively used for replacing 0-50% of the weight of the light-burned magnesium oxide powder in an equivalent manner. Analytically pure citric acid is used as a modifier, and the mixing amount of Citric Acid (CA) is 0.5 percent of the mass of the powder (namely the light-burned magnesia powder and the ground powder). The sand for the test is ISO standard sand, the particle size of the stone for the test is 5-20 mm, and the water for the test is common tap water.

In Table 1, sample numbers Ts5, ts10, ts15, ts20, ts30 and Ts40 correspond to MMOS mortars of examples 1 to 6 in which the amounts of the grinding powders were 5%, 10%, 15%, 20%, 30% and 40%, respectively, and sample numbers Ts0 and Ts50 correspond to MMOS mortars of comparative examples 1 to 2 in which the amounts of the grinding powders were 0% and 50%, respectively.

TABLE 1 mixing ratio (g/L) of the MMOS mortar with different mixing amounts of the grinding powder

In each of examples and comparative examples, mgSO ₄ ·7H ₂ All O is industrial grade magnesium sulfate heptahydrate produced by Tianjin; as for MgO, light-burned magnesia powder produced in Shandong was used, and XRD analysis results thereof are shown in FIG. 3, and it can be seen from FIG. 3 that the content of magnesia is about 80%. FIG. 4 is a graph showing a distribution of particle diameters of a soft-burned magnesia powder and a ground powder in each of examples and comparative examples. As can be seen from FIG. 4, the light-burned magnesia powder has a main particle size distribution of 1 to 2 μm and 20 to 50 μm, and the ground powder has a main particle size distribution of 30 to 70 μm. The chemical compositions of the soft-burned magnesia powder and the milled powder are shown in tables 2 and 3, respectively.

TABLE 2 chemical composition of light-burned magnesia powder (%)

TABLE 3 chemical composition of milled powder (%)

1. In order to explore the high-value resource utilization approach of the heavy metal sludge, the influence and mechanism of the ground powder on the working performance, early free shrinkage deformation, mechanical property, heavy metal leaching behavior and the like of the modified magnesium oxysulfate cement-based material are experimentally researched, and the test scheme is as follows:

(1.1) influence of the ground powder on the fluidity and mechanical properties of the modified magnesium oxysulfate cement-based material

And mixing modified magnesium oxysulfate cement paste of six groups of Ts0, ts5, ts10, ts15, ts20 and Ts30 according to the same water-cement ratio as the mixing ratio in the table 1. And testing the fluidity of the modified magnesium oxysulfate cement paste with different mixing amounts of the grinding powder according to GB/T8077-2000 concrete additive homogeneity test method.

Eight groups of modified magnesium oxysulfate cement mortars are mixed according to the mixing proportion in the table 1, and six groups of three-connected-die test pieces with the sizes of 40mm multiplied by 160mm are formed by the mixing amount of each group. Covering with preservative film for 24h, demoulding, placing the test piece into a room with the temperature of 20 +/-2 ℃ and the humidity of 70 +/-5% for curing to the age of 3d, 7d, 28d, 56d and 90d, and measuring the compressive strength and the flexural strength.

(1.2) influence of the ground powder on early crack resistance and volume stability of the modified magnesium oxysulfate cement concrete

And mixing Ts0, ts10 and Ts40 modified magnesium oxysulfate cement concrete according to the same water-cement ratio as the mixture ratio in the table 1, wherein the sand-stone ratio of each group is 0.61. Two cuboid concrete test pieces with the size of 100mm multiplied by 515mm are formed in each group, the formed test pieces are connected with a non-contact concrete shrinkage deformation tester and then are placed into a room with the temperature of 20 +/-2 ℃ and the humidity of 70 +/-5% for testing, the early plastic shrinkage test is carried out within 24 hours, the reading is carried out once every 1 hour, and the specific operation is carried out according to GB/T50082-2009 test method standard for long-term performance and durability of common concrete.

And mixing Ts0, ts10 and Ts40 groups of modified magnesium oxysulfate cement paste in sequence according to the mixing proportion of the clean paste with the standard consistency obtained by laboratory test mixing. The test pieces are made into round cakes with the diameter of 70-80 mm and the center thickness of 10mm, and two test pieces are formed by each group of mixing amount. The test piece is placed into a boiling box for volume stability test after being maintained indoors for 24 +/-2 hours at the temperature of 20 +/-2 ℃ and the humidity of 70 +/-5 percent, and the specific operation is carried out according to GB/T1346-2011 inspection method of water consumption, setting time and stability of standard consistency of cement.

(1.3) influence of the grinding powder on leaching of heavy metals in the modified magnesium oxysulfate cement-based material

Two groups of modified magnesium oxysulfate cement mortars are mixed according to the mixing ratio of Ts0 and Ts40 in the table 1, and each group is mixed to form a three-connected-die test piece with the size of 40mm multiplied by 160 mm. And curing the demolded test piece to 28d +/-8 h in a room with the temperature of 20 +/-2 ℃ and the humidity of 70 +/-5%. And crushing and grinding the test piece after maintenance, sieving the test piece by using a square-hole sieve, and collecting particles with the particle size of 0.125-0.25 mm as a test sample to be tested. The method comprises the steps of preparing a solution to be tested by using a magnetic stirrer (CJB-S-10D) and a circulating water type multipurpose vacuum pump (SHZ-D (III)), testing the concentration of heavy metals such as Ni, cr, zn, cu and the like in a sample by using an atomic absorption spectrophotometer (TAS-990), and carrying out EDS (EDS energy spectrum) analysis on non-ground powder particles in the test piece doped with the ground powder by using a Hitachi production S-4800 instrument by referring to GB/T30810-2014 (determination method for leachable heavy metals in cement mortar).

(1.4) influence of the grinding powder on the microstructure characteristics of the modified magnesium oxysulfate cement-based material

Two groups of net slurry test pieces Ts0 and Ts30 are respectively formed according to the same water-cement ratio in the mixture ratio of the table 1, and three test pieces with the sizes of 20mm multiplied by 20mm are formed in each group. Maintaining the test piece for 12h, 7d and 56d, then placing the test piece into absolute ethyl alcohol to stop hydration, grinding the test piece fragments with the termination of hydration into powder, performing XRD analysis by using a Purkinjie general Instrument XRD-3 type Cu target X-ray Instrument, and probing the change of the modified magnesium oxysulfate cement hydration product under different mixing amounts of the ground powder. And curing the other part of the test piece to 14d and 28d, putting the test piece into absolute ethyl alcohol to terminate hydration, then performing IR and TG analysis by adopting a Fourier infrared spectrometer and a TA SDT Q600 thermogravimetric analyzer, further verifying the analysis result of the XRD on the hydration product, simultaneously performing a BET adsorption test by adopting a V-sorb2800 instrument, performing SEM analysis by adopting a Nissan product S-4800 scanning electron microscope, and probing the influence of different mixing amounts of the fine powder on the pore structure and the microstructure morphology of the modified magnesium oxysulfate cement.

2. Test results and discussion

(2.1) influence of the ground powder on the fluidity and mechanical properties of the modified magnesium oxysulfate cement-based material

FIG. 5 shows the fluidity of the clean cement paste with different amounts of the grinding powder, and it can be seen from FIG. 5 that the fluidity of the magnesium oxysulfate cement paste is gradually improved with the increase of the amount of the grinding powder, which shows that the ground powder has a significant improvement on the workability of the clean cement paste of MMOS. As can be seen from FIG. 4, the particle size distribution of the milled powder is more uniform than that of the light-burned magnesia powder, when cement particles are uniformly distributed, the particle stacking void ratio is correspondingly small, less free water is needed to fill the voids, the water requirement of the cement is reduced, the rheological property of the cement is improved, and the fluidity of the cement paste is obviously improved. Furthermore, it can be seen from FIG. 4 that the primary particle size of the ground powder is larger than that of the light-burned magnesia powder, and the net slurry fluidity of cement with coarser powder fineness is larger. In terms of micro-morphology, as can be seen from the scanning electron microscope image of the milled powder in fig. 2, the structure of the milled powder is between the crystal and the sphere, and the shape of the milled powder is more regular compared with the shape of the magnesium oxide particles, which is also the reason for obviously improving the fluidity of the net slurry along with the increase of the mixing amount of the milled powder.

FIGS. 6a and 6b show compressive and flexural strengths of MMOS at different amounts of milled powder and at different ages, respectively. As can be seen from FIGS. 6a and 6b, the compressive strength and the flexural strength of the early (3 d) test piece both gradually decreased with the increase of the amount of the milled powder, and particularly, when the amount of the milled powder was more than 30%, the compressive strength and the flexural strength showed a significant slip-down with the increase of the amount of the milled powder. The compressive strength and the flexural strength of the MMOS with the mixing amount of the ground fine powder being 30 percent are respectively reduced by 22.8 percent and 27.7 percent compared with the compressive strength and the flexural strength of the MMOS without the mixing amount of the ground fine powder; the compressive strength and the flexural strength of the MMOS with the mixing amount of the grinding fine powder of 40 percent are respectively reduced by 34.7 percent and 44.9 percent compared with the compressive strength and the flexural strength of the MMOS without the mixing amount of the grinding fine powder. And along with the increase of the age, the reduction degree of the compression strength and the breaking strength of the test piece is gradually reduced by the increase of the mixing amount of the grinding powder. When the curing age is 28 days, the compressive strength and the flexural strength of the MMOS with the mixing amount of the grinding fine powder being 40 percent are respectively reduced by 32.5 percent and 25.7 percent compared with the compressive strength and the flexural strength without the mixing of the grinding fine powder. In the later period of maintenance (90 d), the compressive strength and the flexural strength of the MMOS with the mixing amount of the grinding fine powder being 40 percent are respectively reduced by 23.6 percent and 10.4 percent compared with the compressive strength and the flexural strength of a mortar test piece without the mixing amount of the grinding fine powder. From the data results, it can be seen that the addition of the grinding powder significantly reduces the compressive strength and the flexural strength of the modified magnesium oxysulfate cement mortar specimen at an early stage, while the reduction effect at a later stage becomes insignificant with the increase of the curing time. In the later period, the reduction degree of the compressive strength and the flexural strength can be controlled to be about 10-20% when the mixing amount of the grinding powder is 40%. Meanwhile, the magnesium oxysulfate cement is modified by citric acid, so that the mechanical property of the magnesium oxysulfate cement is superior to that of common Portland cement, and the mechanical property of the MMOS can be well guaranteed when the mixing amount of the grinding powder is controlled within 40%.

(2.2) influence of the ground powder on early free shrinkage deformation and volume stability of the modified magnesium oxysulfate cement concrete

FIG. 7 shows the results of the early free shrinkage deformation test of concrete specimens with different amounts of the finely divided powder. As can be seen from the curves in the graph, when the mixing amount of the grinding powder is increased from 0 to 10 percent, the shrinkage curve change trends of the two groups of concrete samples before 13h are almost completely consistent, but the shrinkage of the test samples mixed with the 10 percent of the grinding powder is obviously reduced after 13 h. At the age of 24 hours, the shrinkage of the test piece doped with 10% of the grinding powder is reduced by 51.8% compared with the shrinkage of the test piece not doped with the grinding powder. And as the mixing amount of the grinding fine powder is continuously increased to 40 percent, the time for the concrete test piece to start to shrink obviously is delayed from about 3.5 hours to about 7.5 hours, and the shrinkage within 7.5 hours to 20 hours is obviously lower than that of the test piece with lower mixing amount. At the age of 24h, the shrinkage of the test piece doped with 10% of the grinding powder is reduced by 57.1% compared with the shrinkage of the test piece not doped with the grinding powder. The early hydration speed of the grinding powder is far lower than that of magnesium oxide, and the consumption of magnesium oxide powder is reduced after the grinding powder is added, so that the early hydration reaction of the system is reduced, the early free shrinkage deformation of the modified magnesium oxysulfate cement-based material is well reduced, and the initial shrinkage time of the modified magnesium oxysulfate cement concrete is delayed along with the increase of the mixing amount of the grinding powder.

FIG. 8 is a diagram showing the state of a test piece of volume stability after boiling 3 hours, in which the amounts of the milled powder incorporated were 0%, 10% and 40%, respectively. As can be seen from FIG. 8, the test piece after boiling has a flat surface and no cracks, which indicates that the poor stability caused by free calcium oxide can not be caused when the grinding powder is added into the modified magnesium oxysulfate cement-based material.

(2.3) influence of the ground powder on the heavy metal leaching of the modified magnesium oxysulfate cement

Table 4 shows the results of the heavy metal leaching concentration test in MMOS with different amounts of milled powder. As can be seen from the numerical values in Table 4, cr element in the mortar test piece doped with the grinding powder is not detected; the leaching concentration of the Ni element is the highest, but the Ni element still meets the relevant standard regulation; the leaching concentrations of the Zn and the Cu are much lower than the standard limit value. Therefore, the grinding powder disclosed by the invention can be safely mixed with cement for practical engineering application.

TABLE 4 heavy metal leaching concentration (mg/L) in MMOS of different amounts of milled powder

ND: not detected out

FIG. 9 is the concentration of heavy metals in different samples. The information in fig. 9 shows that the milled powder has a certain amount of heavy metal content, and the concentration of heavy metal leached by the MMOS is greatly reduced compared with the content of heavy metal carried by the milled powder, which shows that the modified magnesium oxysulfate cement has a better consolidation effect on the heavy metal in the milled powder.

FIG. 10a is an EDS plot of a 28 d-aged MMOS specimen doped with 40% grind, and EDS spectroscopy was performed at the locations indicated by the small boxes in FIG. 10a to obtain the analysis results shown in FIG. 10 b. As can be seen from fig. 10a and 10b, the surface of the MgO particles in the MMOS test piece is consolidated with heavy metal elements such as Zn, cr, ni, etc., wherein the consolidated amounts of Zn and Cr elements are large, which explains why one of these two elements is detected at a low concentration and the other is not detected in table 4; the MgO granules have a low Ni content, and the Ni content in the leaching test is the highest among the heavy metal elements.

(2.4) results of the Effect of the grinding powder on the microstructure characteristics of MMOS

(2.4.1) analysis of the microscopic pore Structure

FIG. 11 is an absorption/desorption curve obtained by nitrogen adsorption (BET) of MMOS test pieces having 0 and 30% of the content of the milled powder. It can be seen from fig. 11 that the isotherms of the two sets of test pieces are concave in the low pressure section, the amount of adsorbed gas increases with the increase of the component partial pressure, a sudden inflection point appears when the relative pressure approaches 0.5, and the isotherms increase uniformly with the increase of the relative pressure in the high pressure section. The curve of low pressure section is recessed because the interact between the adsorbate molecule is than the strong between adsorbate and the adsorbent, and the heat of adsorption of first layer is less than the heat of liquefaction of adsorbate to it is difficult in the absorption to adsorb initial adsorbate, and along with going on of adsorption process, self-acceleration phenomenon appears in the absorption, and the adsorption layer number is unrestricted yet, thereby appears the sudden increase of absorption curve. Therefore, the data when the relative pressure is greater than 0.5 can reflect the more real condition of the test piece, and as can be seen from fig. 11, the adsorption amount of the MMOS test piece doped with 30% of the grinding powder is lower than that of the test piece without the grinding powder.

Table 5 shows the results of the mesoporous analysis of the MMOS test pieces having the amounts of the milled powders of 0% and 30% using the BJH model. As the Kelvin equation adopted by the BJH model is not suitable for micropores with the pore diameter less than 2nm, the experimental result is more accurate for mesopores with the pore diameter greater than 2 nm. From the information in Table 5, it can be seen that, although the average pore diameter and the median pore diameter were higher in the test piece with 30% of the milled powder, the specific surface area was higher in the test piece without the milled powder. This shows that the addition of the milled powder slightly reduced the porosity of the MMOS and also significantly increased the pore size of the MMOS, with an average pore size increase of 31.0% and a median pore size increase of 50.6%. FIG. 12 is the MMOS pore size distribution for different amounts of milling powder, and it can be seen from FIG. 12 that the proportion of 1-10 nm pore size is significantly reduced after the milling powder is added, and the proportion of pores above 35nm is increased.

TABLE 5 MMOS mesoporous analysis results for different amounts of milled powder

(2.4.2) microscopic phase composition analysis

FIG. 13 is a XRD analysis result chart of the modified magnesium oxysulfate cement test pieces in the ages of 12h, 7d and 56d with the solid waste powder mixing amount of 0 and 30%, and it can be seen from the chart that in the case of the three ages, as the mixing amount of the grinding powder increases, 517 phase, mgO and Mg (OH) ₂ The peak of (c) was reduced, while the peaks of the other compounds did not change significantly. It can be seen that the reduction in the amount of the magnesium oxide powder directly results in the 517 phase, mg (OH), produced by hydration thereof ₂ The products are reduced, wherein, phase 517 is the most important cementing material for supporting the MMOC mechanical property,this also explains the reason why the mechanical properties of the test pieces gradually decrease as the amount of the milled powder is reduced. Meanwhile, with the increase of the age of the test piece, the peak value difference of the 517 phase in the test piece doped with the grinding powder and the test piece not doped with the grinding powder is smaller and smaller. Most of the 517 phase is generated in 12h in the test piece with the solid waste powder of 0, but the content of the 517 phase in 12h in the test piece with the 30% doping amount is very low, most of the 517 phase is generated in 12h-7d, when the age reaches 56d, the content of the 517 phase is not greatly different before and after the addition of the grinding fine powder, which indicates that the addition of the grinding fine powder delays the hydration of the magnesium oxysulfate cement, has a large influence on the early strength of the magnesium oxysulfate cement, and has a small influence on the later strength. This also explains that the mechanical properties of the test pieces at the age of 56d and later are reduced less remarkably than those of the 3d and 7d test pieces as the solid waste powder mixing amount is increased.

FIG. 14 shows the IR analysis results of modified magnesium oxysulfate cements at 14d and 28d ages with different amounts of fines. As can be seen from fig. 14: for the modified magnesium oxysulfate cement sample with the addition of 0 of the ground powder, the SO is added along with the increase of the age ₄ ^2- 、CO ₃ ^2- And the peak intensity of the antisymmetric telescopic vibration peak of MgO-H shows an increasing trend; SO for the modified magnesium oxysulfate cement sample with 30% of the mixing amount of the grinding powder ₄ ^2- 、CO ₃ ^2- And MgO-H also show an increasing trend in peak intensity of antisymmetric stretching vibration peak. This shows that the 517 phase content in both samples gradually increased with increasing hydration time, which is consistent with XRD analysis results. For the sample with age of 14d, the SO in the modified magnesium oxysulfate cement sample doped with the ground powder ₄ ^2- 、CO ₃ ^2- The peak intensity of antisymmetric stretching vibration peak of MgO-H is higher than that of the modified magnesium oxysulfate cement sample without the addition of the grinding powder; for the sample with the age of 28d, the peak intensity of the antisymmetric stretching vibration peak of MgO-H in the modified magnesium oxysulfate cement sample doped with the grinding fine powder is higher than that of the cement sample not doped with the grinding fine powder, and SO ₄ ^2- And CO ₃ ^2- The peak intensity of the antisymmetric stretching vibration peak is lower than that of a cement sample without the addition of the grinding powder. The analysis was due to CaSO in the milled powder ₄ Containing SO ₄ ^2- It is caused that in the early stages of hydration,SO in modified magnesium oxysulfate cement sample doped with ground powder ₄ ^2- The peak intensity of the antisymmetric telescopic vibration is higher. In the late stage of hydration, 517 phase is formed in large quantity, and SO in 517 phase ₄ ^2- The content of the total SO ₄ ^2- Most of the content of SO in the modified magnesium oxysulfate cement sample without the addition of the ground powder ₄ ^2- The peak intensity of antisymmetric stretching vibration peak is higher than that of the modified magnesium oxysulfate cement sample doped with the grinding fine powder.

FIG. 15a and FIG. 15b are TG-DTG analysis results of modified magnesium oxysulfate cements at ages of 14d and 28d, respectively. In the figure, the endothermic peak between 350 and 450 ℃ corresponds to Mg (OH) ₂ And the area of the decomposition peak represents the content of the corresponding compound. As can be seen from FIGS. 15a and 15b, the TG-DTG curves of the 30% fines-doped MMOS and the unadditized MMOS at both

age

14d and 28d contained significant Mg (OH) ₂ Peak decomposition and incorporation of 30% of finely ground MMOS Mg (OH) ₂ The peak value of the grinding aid is lower than that of cement without mixing fine powder; the figure shows another endothermic peak at around 100 ℃ corresponding to 517 phase, from which it can be seen that the endothermic peak at 517 phase in MMOS with the addition of the milled powder is lower at 14d, while the peak at 517 phase in MMOS at 28d is significantly higher, only slightly lower than that of MMOS without the addition of the milled powder, indicating that at 28d the hydration is substantially mature with 30% of the milled MMOS and the 517 phase in MMOS without the addition being similar. The results of TG-DTG analysis were consistent with those of XRD analysis.

(2.4.3) microscopic morphology analysis

powder

14d and 28 d. Through the analysis of a scanning electron microscope, unhydrated MgO particles, finely ground powder particles (GP) and needle-rod-shaped 517 phases which are common hydration products of magnesium oxysulfate cement can be observed from each test piece. FIGS. 16a and 16b are the microstructure diagrams of MMOS with 0% and 30% of milling powder content, respectively, at a curing age of 14d, and it is evident from the information in the diagrams that the amount of the needle-shaped 517 phase in the cement doped with 30% of milling powder is less than that in the cement not doped with milling powder, and that the large-pore-size Kong Zhanbi is higher, which is consistent with the results of XRD, IR and BET analyses. And it can be seen in figure 16b that the magnesium oxide particles and 517 phase have a large number of finely divided particles attached to their surfaces, which particles impede and retard the hydration process of the modified magnesium oxysulfate cement. FIGS. 16c and 16d are the MMOS microstructure diagrams of the cement with the addition of 0% and 30% of the grinding powder at the curing age of 28d, respectively, and it can be seen that more significant voids can be observed in the cement with 30% of the grinding powder, while the structure of the modified magnesium oxysulfate cement without the grinding powder is more dense, but the difference in the degree of densification is not as significant as that of 14 d. This also explains the reason why the mechanical properties of modified magnesium oxysulfate cements with different amounts of grinding powders are reduced and the reduction is reduced with the age.

3. Conclusion

(1) The increase of the mixing amount of the grinding fine powder can obviously improve the fluidity of the modified magnesium oxysulfate cement paste. In concrete mixing plants and construction sites, the conditions that the fluidity of the cement-based material is insufficient and an additive needs to be additionally added often exist, and the improvement of the working performance of the cement-based material by the grinding powder can obviously improve the convenience of the on-site construction of the modified magnesium oxysulfate cement. The addition of the grinding powder can obviously reduce the compressive strength and the flexural strength of the modified magnesium oxysulfate cement at an early stage, and the reduction effect at a later stage is not obvious along with the increase of the curing time. When the mixing amount of the grinding powder is controlled within 40 percent, the mechanical property of the modified magnesium oxysulfate cement can be better guaranteed.

(2) Although the grinding powder contains a small amount of CaO, the volume stability of the modified magnesium oxysulfate cement is not deteriorated. The early plastic shrinkage value of the modified magnesium oxysulfate cement concrete can be obviously reduced by adding the fine grinding powder, and the plastic shrinkage value can be reduced by over 50 percent when 10 percent of the fine grinding powder is added. Meanwhile, with the increase of the mixing amount of the grinding powder, the initial shrinkage time of the modified magnesium oxysulfate cement concrete is delayed, and the influence of the mixing amount of the grinding powder on the total early plastic shrinkage value of the modified magnesium oxysulfate cement concrete is small.

(3) Tests show that MMOS cement particles have a consolidation effect on heavy metals such as Ni, cr, zn, cu and the like, and leaching concentrations of four heavy metals in the modified magnesium oxysulfate cement mortar doped with 40% of grinding powder are all lower than the requirements of relevant standards, so that relative safety can be ensured when the grinding powder is applied to a cement-based material.

(4) After analysis through XRD, IR, TG, SEM and the like, the grinding fine powder is wrapped outside magnesium oxide particles after being doped into the modified magnesium oxysulfate cement, the hydration process of the magnesium oxysulfate cement is blocked, and the formation of 517 phase is further reduced and delayed. Meanwhile, the hole structure of the MMOS can be obviously changed by adding the grinding powder, so that the proportion of the hole diameter of 1-10 nm is obviously reduced, and the proportion of the hole diameter of more than 35nm is increased.

Claims

1. The modified magnesium oxysulfate cement containing the heavy metal sludge high-temperature treatment slag is characterized by comprising light-burned magnesium oxide powder, magnesium sulfate heptahydrate, ground powder, water and a modifier, wherein the use amount ratio of the modified magnesium oxysulfate cement to the water is (244-465): 215 (24-245): 187: 2.4, the ground powder is obtained by grinding slag obtained by mixing the heavy metal sludge and building slag and performing high-temperature treatment, the ground powder is used as an active mineral admixture in the preparation of the modified magnesium oxysulfate cement to replace 5-40 wt% of the light-burned magnesium oxide powder in an equivalent manner, and the modifier is a citric acid modifier.

2. The modified magnesium oxysulfate cement comprising the heavy metal sludge high-temperature treatment slag according to claim 1, wherein the ground powder is used as an active mineral admixture in the preparation of the modified magnesium oxysulfate cement to equivalently replace 10-40 wt% of light-burned magnesium oxide powder.

3. The modified magnesium oxysulfate cement containing the heavy metal sludge high-temperature treatment slag charge according to claim 1, wherein the mass ratio of the heavy metal sludge subjected to high-temperature treatment to the building slag soil is 1 (2.5-3.5).

4. The modified magnesium oxysulfate cement containing the heavy metal sludge high-temperature treatment slag charge of claim 1, wherein the high-temperature treatment process is as follows: raising the temperature of the furnace from normal temperature to 1100 ℃, then adding the mixture of the heavy metal sludge and the building residue soil into the furnace, keeping the temperature for 6-8 h, then raising the temperature of the furnace to 1300 ℃, and finally lowering the temperature of the furnace from 1300 ℃ to the normal temperature within 24 h.

5. The modified magnesium oxysulfate cement as claimed in claim 1, wherein the primary particle size of the ground powder is 30 to 70 μm.

6. The use of heavy metal sludge high temperature treatment slag in the modified magnesium oxysulfate cement of claim 1, wherein the slag obtained by high temperature treatment after mixing heavy metal sludge with construction slag is ground into a ground powder, and the ground powder is used as an active mineral admixture to be added into the modified magnesium oxysulfate cement.

7. The application of the heavy metal sludge as claimed in claim 6, wherein the mass ratio of the heavy metal sludge subjected to high-temperature treatment to the construction residue soil is 1 (2.5-3.5).

8. The use according to claim 6, wherein the high temperature treatment process is: raising the temperature of the furnace from normal temperature to 1100 ℃, then adding the mixture of the heavy metal sludge and the building residue soil into the furnace, keeping the temperature for 6-8 h, then raising the temperature of the furnace to 1300 ℃, and finally lowering the temperature of the furnace from 1300 ℃ to the normal temperature within 24 h.

9. Use according to claim 6, wherein the milled powder has a primary particle size of 30 to 70 μm.