KR20070107762A - Making a solid material from an alkaline hydroxide - Google Patents

Abstract

The invention concerns a method for making a solid material from an alkaline metal hydroxide or one of its precursors, including mixing the alkaline hydroxide or one of its precursors with a calcium compound and silicon oxide in the presence of water. The invention also concerns a method for storing waste, the solid material being obtainable by said method as well as the use of said material.

Description

Making a solid material from an alkaline hydroxide

Environmental protection by preventing water, air and soil pollution is of utmost importance. Most wastes, especially industrial wastes, contain a significant amount of alkali metal compounds, such as sodium, potassium, lithium, for example when washing a metal bath.

Alkali metal elements in the waste can cause practical problems during the treatment. For example, they can damage the fire bricks of the incinerator. This problem can be avoided by neutralizing the alkali compound with acidic material by diluting with water or solidifying before treating the cement. However, solidification techniques are problematic because generally only purified water and washed concrete aggregates can be used to produce good quality concrete (Le Beton hydrauliqie, Jacques Baron, Raymond Sauterey, Les Liants mineraux Philippe Pichat, journal). See Technique Moderne n ° 1, 2001, pages 23-31).

The laws and regulations on land placement are strict. In France, wastes are only acceptable if they comply with regulations regarding the pH value of the leachate, the total soluble fraction and the solids content. However, it was observed that sodium hydroxide NaOH resulting from this cement solidification process did not transform into a material with a leachate of less than 13 pH.

It is therefore an object of the present invention to provide a process for the preparation of a solid material from an alkali metal hydroxide or one of its precursors as a solid material in compliance with regulations and in particular Standard X 30417.

The solid material is:

Leachate has a pH of less than 13;

The fraction available is less than 10%;

The solids content is at least 30%;

Metal and phenol concentrations are below certain limits; In that case, compliance with regulations.

The present invention is based on the observation of transforming aqueous solutions of metal alkali hydroxides, calcium salts and silica into solids with very low solubility within a few weeks.

According to the first aspect, the present invention provides:

Mixing the metal alkali hydroxide or one of its precursors with the calcium compound and silica in the presence of water

It provides a method for producing a solid material from one of the metal alkali hydroxide or a precursor thereof.

The metal alkali hydroxide may be lithium, sodium, potassium, rubidium, cesium or francium hydroxide. Preferably, sodium hydroxide or potassium hydroxide.

The term "metal alkali hydroxide precursor" is understood to be a compound capable of forming metal alkali hydroxides in aqueous solution. By way of example, precursors may be listed as carbonates and oxides. Preferably, the precursor is a metal alkali carbonate.

Preferably, the metal alkali hydroxide is in the form of a concentrated aqueous solution, in particular 1 N, or 10 N, in maximum saturation. It may also be in the form of a saturated solution or dispersion.

Preferred calcium compounds are calcium carbonates. However, it may be replaced or mixed with other calcium compounds such as chloride, bromide, sulfate, nitrate or phosphate. According to certain embodiments, the calcium compound and / or the silica is a residue.

The calcium compound is preferably added as a powder. Preferably, the calcium compound is prepared from particles having a particle size of 100% less than 1000 μm, more preferably less than 500 μm, even more preferably less than 100 μm. Chalk is particularly suitable.

The silica is also a powder. Ideally, the silica has a particle size of 100% less than 1000 μm, more preferably less than 500 μm, even more preferably less than 100 μm. Preferably, the silica is present in a different form than quartz with poor reactivity.

However, it may be another form, for example a colloidal solution, which contacts the surface with the solution and thus optimizes the reactivity.

According to a particular embodiment, the calcium compound and silica are added as a silico calcium compound, such as silico calcic sand, fly ashes, bottom ashes, or slag.

The process can be carried out in a continuous mode or batch.

The process operation is very simple and involves contacting a metal alkali hydroxide with a solution of calcium compound and silica.

The reaction rate can be varied within a wide range. For reference, satisfactory results are obtained by adding the reactants in a molar ratio of 0.1 to 10 relative to the metal alkali hydroxide or precursor thereof.

Preferably, 0.1 to 5 moles of calcium compound per mole of metal alkali hydroxide or precursor thereof is preferred. Similarly, 0.1 to 5 moles of silica are added per mole of metal alkali hydroxide or precursor thereof.

Preferably, the various components are mixed for about 5 minutes.

Calcium compounds and silica oxide can be added simultaneously or independently to the metal alkali hydroxide.

According to certain embodiments of the process of the invention, the calcium compound and silica independently disperse the calcium compound and silica in the alkali metal hydroxide or precursor thereof prior to mixing the two dispersions.

The dispersion may or may not be mixed immediately after its preparation. This implementation provides the benefit of reducing the amount of reagent required to solidify the metal alkali hydroxide or its precursor at all the same conditions.

In particular, the amount of the reagent required to solidify 100 parts by weight of 10N NaOH was 39.4 parts by weight of CaCO ₃ (powder <600 μm) and SiO _2. From 80 parts by weight to 27 parts by weight of CaCO ₃ (powder <600 μm) and 70 parts by weight of SiO _2, respectively.

Tobermorite on one hand and Personnite-Gay-Lussite on the other are believed to form.

If no agitation is performed at room temperature, thickening of the calcium compound and silica dispersion is observed. However, the reaction can be promoted by stirring and increasing the temperature.

The viscosity of the mixture increases rapidly. Depending on the concentration of the alkali metal hydroxide and the reactant, the product is obtained in the form of aggregate, putty, dough or grout.

In general, there is no need to provide any additional thermal energy. In general, the reaction is carried out at room temperature for days or weeks.

The resulting product can then be transformed into a monolith product. It can then be shaped by pouring, pomping, compression or vibratory compression.

The method according to the invention is considerable because sodium hydroxide has a high solubility (420 gr / liter) as almost all sodium compounds and is solidified by calcium salts and silica, rather soluble in water and not reactive.

The process according to the invention is simple and very economical, since it only requires low-cost reactants from the quarry. Such manufacturing requires less energy and is not contaminated. According to a preferred embodiment, the calcium compound is obtained from the residue.

Thus, the method of the present invention does not require any thermal energy, any expensive or sophisticated equipment, and does not present any particular risk to people and the environment.

In addition, the method according to the invention does not cause gas or liquid emissions to the environment and is thus environmentally clean.

The process according to the invention can also be used for the coating of other residues to physically and chemically separate them. This variant is very interesting for trapping elements that can be leached.

Indeed, the solution of the solidification process generally contains silico-calcium hydrates having a high surface area of about several hundred m ² / g. This allows to capture the effluent from the waste of the solidification product.

According to another aspect, the present invention is:

Mixing the alkali metal hydroxide or its precursor, calcium compound and silica in the presence of water;

Infiltrating waste into the mixture;

Physically and chemically separating the waste in the solidified mixture;

Transforming the obtained solids into monolithic products;

It provides a method of storing a solid waste, which is insoluble in water.

The waste may be in any form. Preferably, these are graphite pieces. In particular, the waste is toxic and / or radioactive waste in accordance with laws and regulations.

Preferably, the solid material obtained is in accordance with French regulations for waste land placement.

In particular, the solid material is preferably:

Leachate with a pH of less than 13;

Less than 10% soluble fraction;

A solids content of at least 30%; And

-Heavy metal and carbon concentrations below certain limits;

Indicates.

According to another aspect, the invention aims at a solid material obtained by the process disclosed above. The rate of solidification of the product is very sufficient for use and storage immediately after preparation. The product obtained can thus be stored directly.

The solid material can then be used at construction sites for work such as grouts, slabs, rods or for filling a recess or prefabricated plant, for example. It may also be located in a final waste storage facility or in a technical landfill centre.

In accordance with the last aspect, the present invention aims at the use of solidification products obtained for the construction work and the storage of solid waste in building and public works.

Hereinafter, the present invention will be described with reference to Examples, which do not limit the present invention.

Example 1

To 1000 kg of a 16.7 N sodium hydroxide solution was added 700 kg of calcium chloride in the form of industrial residue and 640 kg of silica generated from a quarry with a particle size of 100% and less than 1000 μm. After 28 days of aging, a solid material was obtained. It was subjected to a leaching test according to Standard X 30417 for 24 hours. The pH of the solution was less than 13, the soluble fraction was less than 10% and the solids content was 35% by weight or more.

Example 2

To 1000 kg of 10N sodium hydroxide solution was added 1100 kg of calcium carbonate powder with a particle size of less than 100% 500 μm and 623 kg of silica in the form of an industrial residue having a particle size of 100%, 1500 microns. After 28 days of aging, a solid material was obtained. This was subjected to a leaching test according to Standard X 31212 for 24 hours. The pH of the solution was less than 13, the soluble fraction was less than 10 and the solids content was at least 35% by weight.

Example 3

To 1000 kg of 10N sodium hydroxide solution was added 990 kg of calcium carbonate powder having a particle size of less than 100% 500 microns and 625 kg of silica in the form of an industrial residue having a particle size of 100%, 500 microns. After 28 days of aging, a solid material was obtained. This was subjected to a leaching test according to Standard X 31212 for 24 hours. The pH of the solution was less than 13, the soluble fraction was less than 10 and the solids content was at least 35% by weight.

Example 4

A graphite cylinder having a diameter of 135 mm, a height of 600 mm and a weight of 11 kg was infiltrated into the fresh solution prepared according to Example 2. The matrix is provided by solidifying the physical and chemical separation materials and simultaneously trapping with contaminants, such as radioisotopes, which may be contained in the graphite.

Example 5

100 kg of NaOH (in the form of a 10N solution) was mixed with 33 kg of silica and contacted for 6 days. Then, 35 kg of calcium carbonate extracted from the quarry with a particle size of 100% and less than 600 microns was added. Materials complying with Standard X 30417 were obtained with a total of 68 kg of reactant against 100 kg of metal alkali hydroxide.

Example 6

100 kg of NaOH (in the form of a 10N solution) was mixed with 27 kg of calcium carbonate extracted from a quarry with a particle size of 100% and less than 600 microns and contacted for 3 days. Then 35 kg of silica was added. Materials complying with Standard X 30417 were obtained with 62 kg of reactant against 100 kg of metal alkali hydroxide.

Example 7

100 kg of NaOH (in the form of a 10N solution) was mixed with 27 kg of calcium carbonate and contacted for one day. In a suitable second container, 100 kg of NaOH (in the form of a 10N solution) was mixed with 24 kg of silica and contacted for 3 days. Materials complying with Standard X 30417 were obtained with 51 kg of reactant for 100 kg of metal alkali hydroxide.

Claims (10)

Mixing the hydroxide with the calcium compound and silica in the presence of water; Infiltrating waste into the mixture; Physically and chemically separating the waste from the solidified mixture; And Transforming the obtained solid material into a monolith product; Waste storage method comprising a. The method of claim 1, wherein the calcium compound and silica are dispersed independently in alkali metal hydroxides or precursors thereof prior to mixing the two dispersions. The method of claim 1 or 2, wherein 0.1 to 5 moles of calcium compound is added per mole of alkali metal hydroxide or precursor thereof. 4. A process according to any one of claims 1 to 3, wherein 0.1 to 5 moles of silica are added per mole of alkali metal hydroxide or precursor thereof. The method of claim 1, wherein the solid material has leachate having a pH of less than 13. The method of any one of claims 1 to 5, wherein the solids have less than 10% soluble fraction. The method of claim 1, wherein the solid material has a solids content of at least 30%. The method of claim 1, wherein the waste is a piece of graphite. Monolithic product obtainable by the process according to claim 1. Use of the monolithic product according to claim 9 for the construction of construction and public works and for the storage of solid waste.