1. The application of the carbide slag in preparing the binder.

2. A preparation method of the adhesive is characterized by comprising the following steps,

mixing the carbide slag and the tartrate solution, uniformly stirring, taking a lower-layer solid product, and drying to obtain a binder;

wherein the pH value of the tartrate solution is more than or equal to 13.

3. The preparation method according to claim 2, characterized in that sodium hydroxide is used as a pH regulator to adjust the pH of the tartaric acid solution to obtain a tartrate solution with the pH being more than or equal to 13;

the tartaric acid solution contains tartaric acid 5-10 wt%.

4. The preparation method according to claim 3, wherein the mass ratio of the carbide slag to the tartaric acid solution is 1: (3-10).

5. A binder prepared by the method of any one of claims 2 to 4.

6. A method for preparing red mud pellets, which is characterized in that the binder prepared by the preparation method of any one of claims 2 to 4 or the binder of claim 5 comprises the following steps,

the red mud is mixed with the binder, and the red mud pellets are obtained after cold pressing treatment and drying.

7. The preparation method according to claim 6, wherein the mass ratio of the binder to the red mud is (2-3): 50;

the method also comprises the step of crushing the red mud to obtain red mud particles before mixing the red mud with the binder;

among the crushed red mud particles, the red mud particles with the particle size of less than 2mm account for at least 80 percent of the mass of the red mud.

8. The preparation method according to claim 7, characterized by further comprising the step of adding water when mixing the red mud with the binder;

the addition amount of the water is 8-12% of the mass of the red mud.

9. The red mud pellets produced by the method of any one of claims 6 to 8.

10. Use of the red mud pellets prepared by the method of any one of claims 6 to 8 or the red mud pellets of claim 9 as a slagging agent in converter steelmaking.

Background

The carbide slag is waste slag produced in the production of acetylene, an important chemical raw material, by using carbide, and mainly contains calcium hydroxide, inorganic substances such as calcium carbonate, sulfide, oxides and hydroxides of metals such as magnesium and iron, and a small amount of organic substances. The calcium carbide waste residue belongs to general industrial solid waste, and long-term accumulation not only occupies a large amount of land, but also has serious erosion influence on the land. Changing the carbide slag into valuable is beneficial to the sustainable development of the whole industry. At present, the comprehensive utilization of carbide slag mainly comprises the steps of preparing building materials and using the carbide slag as a roadbed raw material, so that the harm of the waste slag to the environment is reduced, and the road cost can be reduced.

In the prior art, when the carbide slag is used for making bricks, the carbide slag and the fly ash are generally used as main raw materials, auxiliary materials are added, and the bricks without burning the carbide slag are obtained through curing, but the carbide slag serving as the raw materials is limited in adding amount and is difficult to completely digest for enterprises with large slag discharge amount, so that the carbide slag bricks are limited in market sale, and the exertion of products is restricted. The carbide slag is used as a raw material to prepare carbide slag cement, the proportion of the water vapor in kiln waste gas is increased due to the water vapor generated during the decomposition of calcium hydroxide, the service life and the efficiency of the electrostatic dust collector are influenced, and the competitiveness of the cement produced by the carbide slag is not strong. When the carbide slag is used for preparing the calcium carbide, a large amount of energy is consumed, the regenerated stone is reused as the raw material of the calcium carbide, and can only be mixed into 20 percent of the raw material of the calcium carbide without excess, otherwise, the recovered lime contains more impurities, the quality of the calcium carbide is influenced, and the calcium carbide is not suitable for popularization and use. In addition, along with the enhancement of public awareness of energy conservation and environmental protection, the requirement on recycling waste residues and the like is more strict, and the development of the carbide slag is limited due to the great change of one-time historical structural adjustment in the building material and chemical industry. The development and research of a new application of the carbide slag have important significance for realizing the reutilization of the carbide slag.

Disclosure of Invention

Therefore, the invention aims to overcome the defects that the energy consumption is high, the product produced by using the carbide slag as a raw material is limited and the like in the process of recycling the carbide slag in the prior art, and provides the binder and the preparation method and application thereof.

Therefore, the invention provides the following technical scheme.

The invention provides an application of carbide slag in preparing a binder.

The invention provides a preparation method of a binder, which comprises the following steps,

mixing the carbide slag and the tartrate solution, uniformly stirring, taking a lower-layer solid product, and drying to obtain a binder;

wherein the pH value of the tartrate solution is more than or equal to 13.

Adjusting the pH of the tartaric acid solution by using sodium hydroxide as a pH regulator to obtain a tartrate solution with the pH being more than or equal to 13;

the tartaric acid solution contains tartaric acid 5-10 wt%.

And (3) after the pH value of the tartaric acid solution is adjusted, forming a tartrate solution, wherein the mass ratio of the carbide slag to the tartaric acid solution is 1: (3-10).

The drying temperature is 60-80 ℃.

The invention also provides the adhesive prepared by the preparation method.

In addition, the invention also provides a preparation method of the red mud pellets, the binder prepared by the preparation method or the binder comprises the following steps,

the red mud is mixed with the binder, and the red mud pellets are obtained after cold pressing treatment and drying.

The mass ratio of the binder to the red mud is (2-3): 50;

the method also comprises the step of crushing the red mud to obtain red mud particles before mixing the red mud with the binder;

among the crushed red mud particles, the red mud particles with the particle size of less than 2mm account for at least 80 percent of the mass of the red mud.

When the red mud is mixed with the binder, the method also comprises the step of adding water;

the addition amount of the water is 8-12% of the mass of the red mud.

In the cold pressing treatment, the maximum pressure between the pair rollers is 800-²The linear velocity is 0.5-0.8 m/s.

The water content in the red mud is lower than 8 wt%.

The water content in the red mud pellets is lower than 5 wt%.

Further, the invention provides the red mud pellets prepared by the method.

Furthermore, the invention provides the red mud pellets prepared by the method or the application of the red mud pellets as a slagging agent in converter steelmaking.

The technical scheme of the invention has the following advantages:

1. the preparation method of the binder comprises the following steps of mixing carbide slag and tartrate solution, stirring uniformly, taking a lower-layer solid product, and drying to obtain the binder; wherein the pH value of the tartrate solution is more than or equal to 13. The method provided by the invention can enable tartrate radicals to be adsorbed on the surface of the carbide slag under a strong alkaline condition, the tartaric acid and the carbide slag have good complexing ability and adsorption performance, and the obtained binder has good bonding effect. When the pH value is lower than 13, tartaric acid and carbide slag are subjected to chemical reaction to generate calcium tartrate, and the binder cannot play a binding role and has a poor binding effect. According to the invention, the carbide slag and the tartaric acid are used as raw materials, and the pH value of the tartaric acid solution is adjusted, so that the binder with good binding property can be obtained, and the carbide slag can be recycled.

The preparation method of the binder provided by the invention has the advantages of easily available raw materials, capability of changing waste into valuable, great significance for sustainable development of mineral resources, simple process, low energy consumption and small occupied area.

2. According to the preparation method of the red mud pellets, the red mud pellets prepared by using the binder as a raw material have high strength and can meet the production requirement. On one hand, the binder obtained by the carbide slag and the tartrate solution has hydroxyl and carboxyl, and the hydroxyl and the carboxyl can perform complex reaction with iron and calcium in the red mud; on the other hand, the existence of hydroxyl can make the adhesive have better viscosity and enhance the strength of the red mud pellets.

In the prior art, fly ash is usually used as a binder of red mud pellets, but when the pellets are prepared by using the fly ash as the binder of the red mud pellets, the strength cannot meet the use requirement, and the binder prepared by using carbide slag as a raw material can overcome the defect that the fly ash is used as the pellet binder and improve the strength of the pellets.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is a flow chart for preparing a binder in example 1 of the present invention;

FIG. 2 is an infrared spectrum of tartaric acid, carbide slag and a binder according to example 1 of the present invention;

FIG. 3 is an XPS spectrum of carbide slag of example 1 of the present invention;

FIG. 4 is an XPS spectrum of the binder obtained in example 1 of the present invention.

Detailed Description

The following examples are provided to further understand the present invention, not to limit the scope of the present invention, but to provide the best mode, not to limit the content and the protection scope of the present invention, and any product similar or similar to the present invention, which is obtained by combining the present invention with other prior art features, falls within the protection scope of the present invention.

The examples do not show the specific experimental steps or conditions, and can be performed according to the conventional experimental steps described in the literature in the field. The reagents or instruments used are not indicated by manufacturers, and are all conventional reagent products which can be obtained commercially.

Example 1

This example provides a binder and a method for preparing the same, wherein the preparation process is shown in fig. 1, the method comprises the following steps,

adding a sodium hydroxide aqueous solution into a 10 wt% aqueous solution of 800kg of tartaric acid to adjust the pH to 13, stirring and mixing the obtained solution with 80kg of acetylene sludge sieved by a 200-mesh sieve after the pH is adjusted, taking a lower-layer solid product, drying at 70 ℃, and sieving by the 200-mesh sieve to obtain the binder.

The embodiment also provides a red mud pellet and a preparation method thereof, the preparation method comprises the following steps,

crushing red mud to obtain red mud particles, sieving with a 3mm sieve, crushing the oversize materials again to make the red mud particles smaller than 2mm at least reach 90%, uniformly mixing 1000kg of undersize materials with 50kg of the binder, spraying 100kg of water on the uniformly mixed materials, conveying the materials to a feed inlet of a ball press machine for cold pressing treatment, wherein the maximum pressure between rollers is 950t, and the maximum linear pressure ratio is 9.5t/cm²And (3) screening the red mud pellets by a 3cm sieve after cold pressing treatment at the linear velocity of 0.6m/s, drying the oversize products to obtain the red mud pellets, and returning the undersize products to a feed inlet of a ball press machine for cold pressing treatment again.

FIG. 2 is an infrared spectrum of tartaric acid, carbide slag and binder at 1398cm^-1And 1578cm^-1The peak at the position is the characteristic peak of the carbonyl group, indicating that a reaction between tartaric acid and calcium cations has occurred. 1079cm^-1The position belongs to the stretching vibration of C-O, which shows that the hydroxyl of the tartaric acid is adsorbed on the carbide slag.

FIG. 3 is an XPS spectrum of carbide slag, and FIG. 4 is an XPS spectrum of the binder obtained in this example. In fig. 3, Ca2p in the carbide slag is Ca — O, and after tartaric acid is adsorbed, as shown in fig. 4, the spectrum of Ca2p can be decomposed into three separate peaks: Ca-O (348.6 and 352.1eV), C-O-Ca (346.7 and 350.2eV) and COO-Ca (347.7 and 351.2eV) indicate that Ca ions in the carbide slag are complexed with hydroxyl groups in the tartaric acid, and the tartaric acid is adsorbed on the carbide slag, which is consistent with the graph in FIG. 2. The tartaric acid is mainly adsorbed on the carbide slag through the complexation reaction between hydroxyl and carboxyl and calcium ions.

Example 2

This example provides a binder and a method for preparing the same, the method comprising the steps of,

adding sodium hydroxide aqueous solution into 360kg of tartaric acid aqueous solution 6.67 wt% to adjust the pH to 13, stirring and mixing the obtained solution with 60kg of acetylene sludge sieved by a 200-mesh sieve after the pH is adjusted, taking a lower-layer solid product, drying the product at 80 ℃, and sieving the product by the 200-mesh sieve to obtain the binder.

The embodiment also provides a red mud pellet and a preparation method thereof, the preparation method comprises the following steps,

crushing red mud to obtain red mud particles, sieving with a 3mm sieve, crushing oversize materials again to make the red mud particles smaller than 2mm at least reach 90%, uniformly mixing 1000kg of undersize materials with 50kg of the binder, spraying 80kg of water on the uniformly mixed materials, conveying the materials to a feed inlet of a ball press machine for cold pressing treatment, wherein the maximum pressure between rollers is 800t, and the maximum linear pressure ratio is 8t/cm²And (3) screening the red mud pellets by a 3cm sieve after cold pressing treatment at the linear velocity of 0.6m/s, drying the oversize products to obtain the red mud pellets, and returning the undersize products to a feed inlet of a ball press machine for cold pressing treatment again.

Example 3

This example provides a binder and a method for preparing the same, the method comprising the steps of,

adding a sodium hydroxide aqueous solution into 560kg of tartaric acid aqueous solution with the weight percentage of 6.25 to adjust the pH value to 13, stirring and mixing the obtained solution with 70kg of acetylene sludge sieved by a 200-mesh sieve after the pH value is adjusted, taking a lower-layer solid product, drying the product at 60 ℃, and sieving the product by the 200-mesh sieve to obtain the binder.

The embodiment also provides a red mud pellet and a preparation method thereof, the preparation method comprises the following steps,

crushing red mud to obtain red mud particles, sieving with a 3mm sieve, crushing the oversize materials again to make the red mud particles smaller than 2mm at least reach 90%, uniformly mixing 1000kg of undersize materials with 50kg of the binder, spraying 80kg of water on the uniformly mixed materials, conveying the materials to a feed inlet of a ball press machine for cold pressing treatment, wherein the maximum pressure between rollers is 850t, and the maximum linear pressure ratio is 8.5t/cm²And (3) screening the red mud pellets by a 3cm sieve after cold pressing treatment at the linear velocity of 0.8m/s, drying the oversize products to obtain the red mud pellets, and returning the undersize products to a feed inlet of a ball press machine for cold pressing treatment again.

Example 4

This example provides a binder and a method for preparing the same, the method comprising the steps of,

adding aqueous solution of sodium hydroxide into aqueous solution of tartaric acid (7.5 wt%) and (640 kg) to adjust pH to 13, stirring and mixing with acetylene sludge (80 kg) passing through a 200-mesh sieve, taking the solid product of the lower layer, drying at 70 ℃, and passing through a 200-mesh sieve to obtain the binder.

The embodiment also provides a red mud pellet and a preparation method thereof, the preparation method comprises the following steps,

crushing red mud, sieving with a 3mm sieve, crushing oversize again to make the red mud particle ratio less than 2mm at least reach 90%, uniformly mixing 1000kg undersize with 40kg of the binder, spraying 100kg of water on the uniformly mixed material, and sending to a feed inlet of a ball press for cold pressing treatment, wherein the maximum pressure between rollers is 900t, and the maximum linear pressure ratio is 9t/cm²And (3) screening the red mud pellets by a 3cm sieve after cold pressing treatment at the linear velocity of 0.6m/s, drying the oversize products to obtain the red mud pellets, and returning the undersize products to a feed inlet of a ball press machine for cold pressing treatment again.

Example 5

This example provides a binder and a method for preparing the same, the method comprising the steps of,

adding a sodium hydroxide aqueous solution into 560kg of tartaric acid aqueous solution with the weight percentage of 7.5 to adjust the pH value to 13, stirring and mixing the obtained solution with 70kg of acetylene sludge sieved by a 200-mesh sieve after the pH value is adjusted, taking a lower-layer solid product, drying the product at 70 ℃, and sieving the product by the 200-mesh sieve to obtain the binder.

The embodiment also provides a red mud pellet and a preparation method thereof, the preparation method comprises the following steps,

crushing red mud, sieving with a 3mm sieve, crushing oversize again to make the red mud particle ratio less than 2mm at least reach 90%, mixing 1000kg undersize with 50kg of the above binder, spraying 120kg of water on the uniformly mixed material, sending to a feed inlet of a ball press for cold pressing treatment, wherein the maximum pressure between rollers is 1000t, and the maximum linear pressure ratio is 10t/cm²And (3) screening the red mud pellets by a 3cm sieve after cold pressing treatment at the linear velocity of 0.5m/s, drying the oversize products to obtain the red mud pellets, and returning the undersize products to a feed inlet of a ball press machine for cold pressing treatment again.

Example 6

This example provides a binder and a method for preparing the same, the method comprising the steps of,

adding a sodium hydroxide aqueous solution into a 10 wt% aqueous solution of 800kg of tartaric acid to adjust the pH to 13, stirring and mixing the obtained solution with 80kg of acetylene sludge sieved by a 200-mesh sieve after the pH is adjusted, taking a lower-layer solid product, drying at 70 ℃, and sieving by the 200-mesh sieve to obtain the binder.

The embodiment also provides a red mud pellet and a preparation method thereof, the preparation method comprises the following steps,

crushing red mud, sieving with a 3mm sieve, crushing oversize again to make the red mud particle ratio less than 2mm at least reach 90%, mixing 1000kg undersize with 60kg of the above binder, spraying 100kg of water on the uniformly mixed material, and sending to a feed inlet of a ball press for cold pressing treatment, wherein the maximum pressure between rollers is 950t, and the maximum linear pressure ratio is 9.5t/cm²And (3) screening the red mud pellets by a 3cm sieve after cold pressing treatment at the linear velocity of 0.6m/s, drying the oversize products to obtain the red mud pellets, and returning the undersize products to a feed inlet of a ball press machine for cold pressing treatment again.

Comparative example 1

The present comparative example provides a binder and a method for preparing the same, the method comprising the steps of,

adding a sodium hydroxide aqueous solution into a 10 wt% aqueous solution of 800kg of tartaric acid to adjust the pH to 12, stirring and mixing the obtained solution with 80kg of acetylene sludge sieved by a 200-mesh sieve after adjusting the pH, taking a lower-layer solid product, drying at 70 ℃, and sieving by the 200-mesh sieve to obtain the binder.

The embodiment also provides a red mud pellet and a preparation method thereof, the preparation method comprises the following steps,

crushing red mud to obtain red mud particles, sieving with a 3mm sieve, crushing the oversize materials again to make the red mud particles smaller than 2mm at least reach 90%, uniformly mixing 1000kg of undersize materials with 50kg of the binder, spraying 100kg of water on the uniformly mixed materials, conveying the materials to a feed inlet of a ball press machine for cold pressing treatment, wherein the maximum pressure between rollers is 950t, and the maximum linear pressure ratio is 9.5t/cm²And (3) screening the red mud pellets by a 3cm sieve after cold pressing treatment at the linear velocity of 0.6m/s, drying the oversize products to obtain the red mud pellets, and returning the undersize products to a feed inlet of a ball press machine for cold pressing treatment again.

Comparative example 2

The present comparative example provides a binder and a method for preparing the same, the method comprising the steps of,

adding a sodium hydroxide aqueous solution into a 10 wt% aqueous solution of 800kg of tartaric acid to adjust the pH to 8, stirring and mixing the obtained solution with 80kg of acetylene sludge sieved by a 200-mesh sieve after adjusting the pH, taking a lower-layer solid product, drying at 70 ℃, and sieving by the 200-mesh sieve to obtain the binder.

The embodiment also provides a red mud pellet and a preparation method thereof, the preparation method comprises the following steps,

crushing red mud to obtain red mud particles, sieving with a 3mm sieve, crushing the oversize materials again to make the red mud particles smaller than 2mm at least reach 90%, uniformly mixing 1000kg of undersize materials with 60kg of the binder, spraying 100kg of water on the uniformly mixed materials, conveying the materials to a feed inlet of a ball press machine for cold pressing treatment, wherein the maximum pressure between rollers is 950t, and the maximum linear pressure ratio is 9.5t/cm²And (3) screening the red mud pellets by a 3cm sieve after cold pressing treatment at the linear velocity of 0.6m/s, drying the oversize products to obtain the red mud pellets, and returning the undersize products to a feed inlet of a ball press machine for cold pressing treatment again.

Comparative example 3

The present comparative example provides a binder and a method for preparing the same, the method comprising the steps of,

adding a sodium hydroxide aqueous solution into a 10 wt% aqueous solution of 800kg of tartaric acid to adjust the pH to 3, stirring and mixing the obtained solution with 80kg of acetylene sludge sieved by a 200-mesh sieve after adjusting the pH, taking a lower-layer solid product, drying at 70 ℃, and sieving by the 200-mesh sieve to obtain the binder.

The embodiment also provides a red mud pellet and a preparation method thereof, the preparation method comprises the following steps,

crushing red mud, sieving with a 3mm sieve, crushing oversize again to make the red mud particle ratio less than 2mm at least reach 90%, mixing 1000kg undersize with 50kg of the above binder, spraying 100kg of water on the uniformly mixed material, and sending to a feed inlet of a ball press for cold pressing treatment, wherein the maximum pressure between rollers is 950t, and the maximum linear pressure ratio is 9.5t/cm²The linear velocity is 0.6m/s, the red mud pellets are obtained after the cold pressing treatment and the drying of the oversize material after passing through a 3cm sieve, and the undersize material returns to the feeding port of the ball press and is cold pressed againAnd (6) processing.

Comparative example 4

The present comparative example provides a binder and a method for preparing the same, the method comprising the steps of,

adding a sodium hydroxide aqueous solution into a 10 wt% citric acid aqueous solution of 800kg to adjust the pH to 13, stirring and mixing the solution with 80kg of acetylene sludge sieved by a 200-mesh sieve after the pH is adjusted, taking a lower-layer solid product, drying at 70 ℃, and sieving by the 200-mesh sieve to obtain the binder.

The embodiment also provides a red mud pellet and a preparation method thereof, the preparation method comprises the following steps,

crushing red mud, sieving with a 3mm sieve, crushing oversize again to make the red mud particle ratio less than 2mm at least reach 90%, mixing 1000kg undersize with 50kg of the above binder, spraying 100kg of water on the uniformly mixed material, and sending to a feed inlet of a ball press for cold pressing treatment, wherein the maximum pressure between rollers is 950t, and the maximum linear pressure ratio is 9.5t/cm²And (3) screening the red mud pellets by a 3cm sieve after cold pressing treatment at the linear velocity of 0.6m/s, drying the oversize products to obtain the red mud pellets, and returning the undersize products to a feed inlet of a ball press machine for cold pressing treatment again.

Comparative example 5

The present comparative example provides a binder and a method for preparing the same, the method comprising the steps of,

adding a sodium hydroxide aqueous solution into 10 wt% of 800kg of malic acid aqueous solution to adjust the pH value to 13, stirring and mixing the solution with 80kg of acetylene sludge sieved by a 200-mesh sieve after adjusting the pH value, taking a lower-layer solid product, drying at 70 ℃, and sieving by the 200-mesh sieve to obtain the binder.

The embodiment also provides a red mud pellet and a preparation method thereof, the preparation method comprises the following steps,

crushing red mud, sieving with a 3mm sieve, crushing oversize again to make the red mud particle ratio less than 2mm at least reach 90%, mixing 1000kg undersize with 50kg of the above binder, spraying 100kg of water on the uniformly mixed material, and sending to a feed inlet of a ball press for cold pressing treatment, wherein the maximum pressure between rollers is 950t, and the maximum linear pressure ratio is 9.5t/cm²Cold pressing at 0.6m/s, sieving with 3cm sieve, and drying to obtain the final productAnd returning the sieved materials to a feeding port of the ball press to carry out cold pressing treatment again when the red mud pellets are obtained.

Test examples

The test example provides performance tests and test results of the binders and red mud pellets obtained in examples 1-6 and comparative examples 1-5.

The method for testing the strength of the red mud pellets comprises the following steps: the dried red mud pellets are placed on the surface of a steel plate of a universal tester, and the red mud pellets are radially compressed by a pressure head with the diameter of 10.00cm at the speed of 5.00 mm/min. The sensor records the force applied by the pressure head in real time, and the maximum load of the red mud pellet material is recorded as the compressive strength (N/P). And randomly selecting 15 red mud pellets in each batch for testing, and averaging to obtain the strength of the red mud pellets.

The method for testing the water content of the red mud pellets comprises the following steps: the red mud pellets obtained in each example and comparative example were weighed (M)₁) It was dried in an oven at 50 ℃ until constant weight and weighed again (M)₂) Calculating the water content of the red mud pellets, wherein the unit is; wherein, the water content is calculated by the following formula,

table 1 performance test results of red mud pellets

As can be seen from the results in table 1, the experimental results of comparative examples 1 to 3 show that the pH of the tartaric acid solution has a large influence on the strength of the red mud pellets, and the strength of the red mud pellets is low when the binder obtained from the tartrate solution having a pH lower than 13 is used as a raw material of the pellets. The results of comparative examples 4-5 demonstrate that the strength of the red mud pellets is also reduced by changing tartaric acid to citric acid or malic acid.

In the invention, tartaric acid solution and carbide slag act under a strong alkaline condition, the obtained binder has good binding effect, and the red mud pellets prepared by using the binder as a raw material have good strength.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the spirit or scope of the invention.