IE83507B1 - Process for the insolublization and agglommeration of loose incineration ash - Google Patents

Abstract

ABSTRACT Fly ash from incineration (FA) is mixed with small quantities of water of between 10% and 35% of its weight, the product being subsequently compacted and extruded. In practice it is advantageous to add small quantities of lime to the water to have a pH of (7.4) to (11.6), it being possible for this lime to be associated with a product containing silica and/or alumina. Solid compositions which are practically insoluble in water and nonpolluting are obtained.

Description

PROCESS FOR THE IN SOLUB ILIZATION AND AGGLOMERATION OF LOOSE INCINERATION ASH PHILIPPE PICHAT The present invention relates to the field of waste treatment with a View to rendering it insoluble and transforming it into a compact mass trapping the toxic elements and products, notably metals. It is applied quite particularly to the case of loose incineration ash.

It is known that loose incineration ash (hereinafter called CV by way of abbreviation) is the result of the combustion of all types of waste. Apart from clinker and smoke purification waste, an incinerator produces a large quantity of CV in the form of fine particles which are trapped, generally, by electrostatic means. The composition of the CV varies, of course, as a function of the type of waste, the equipment used and the operating conditions. In the case of household refuse incineration, for instance, the composition of a CV is approximately as follows: Si 223%; Al: 7%; Fe 4%; Pb : l%; Zn: 1.9%; Ca: 8%; Mg : 2.5% ; Ba : 0.3% ; K : 4% ; Na : 3% ; Ti : 0.7% ; Cd : 0.03% ; Sn : 0.3% ; Cr : O.l% ; Cl : % , S %; Na : 3% ; N 4% , P 5% , organic C about 1% of the residue.

CV stored in a humid environment can cause substantial pollution due to leaching. Thus it is, for instance, .8, that a representative sample of a pH of about subject to DIN 38414, releases the following toxic elements by leaching (quantities in parts per million p.p.m.) : Pb 6.3 ; Cu 0.2 ; Cd : 60 ; Zn 900 ; Fe .2.

The document US—A—4 472 198 describes a process for treating loose ash in which said ash is mixed with to 25% by weight of water, the mixture obtained then being compacted. Thanks to this process a product resembling earth is obtained.

Moreover, a certain number of processes have been suggested for rendering loose incineration ash insoluble, for instance by adding to it lime in substantial quantities, or more cement or mixtures of cement and sodium silicate. The compositions obtained by such treatments are very basic than 12) (pH generally higher and have a tendency to solubilise elements such as lead and zinc in particular. Another disadvantage may arise, namely the premature production of hydrogen according to the reaction OH” + H20 + Al ——————— ——> A102‘ + 3/2 H2.

With the aim of avoiding these disadvantages, due for the most part to the strong basicity of the treated CV, the applicant has carried out numerous experiments intended to transform the CV into products practically insoluble in water and easy to agglomerate into masses or even suitable for use in which are inert, non—toxic, concretes.

First of all it has been found, surprisingly, that products with the above characteristics could be obtained by adding to the CV a small quantity of water so as to obtain a mortar or a paste or, better still, a mass simply moistened homogenously with water.

To achieve suitable moistening the moistening operation can be carried out in a mixing machine or on a conveyor belt on which the CV travels and over which at least a part of the necessary water is scattered.

This quantity of water can vary generally between the limits of 10 to 35% by weight of the CV but it often turns out to be in the region of 10 to 18%.

According to an interesting method of carrying out the process of the invention, instead of using ordinary water one can use a non—purified water such as, for instance, surface or underground water, waste water, mud from a water—purifying station or even discharged leachates.

After treatment in the above conditions the mixture obtained no longer emits dust and is carefully compacted in the form of parpens or the like or by one of the devices used in public works. According to one variant such mixtures can also be extruded.

It was possible to establish, during these operations to moisten the CV and by various analyses, notably by diffraction with X—rays, that the water added to the CV behaved like a real reagent, with the formation, in particular, of gehlenite of the formula (CaO)2, Al2O3, Slog, 8H2O, and of aluminate (CaO)4, Alxh, 13 H20, the water added becoming part of the water consituting these products.

The experiment results, summarised in table 1 below, in accordance with DIN l4, show that the leaching, for a CV with a pH of about 7.6 treated according to the invention is considerably diminished.

Table 1 Metals Pb Cu Cd Zn Fe water/CV ratio before treatment 6.3 0.2 60 900 0.2 0 after treatment 0.4 <0.1 1.5 0.1 0.30 0.35 <0.1 0.1 0.1 0.15 The values indicated above are expressed in ppm of metals.

As can be seen a low water/CV ratio encourages the fixing of the pollutant elements. This ratio corresponds generally to a minimum of 0.13 to 0.14 but it can be still slightly lowered by the use of fluidising agents such as, for instance, lignosulphates.

It has also been found that in the fairly frequent case where one is dealing with acidic CV’s the results after leaching as well as the tendency to obtain hard waste masses were still further improved when a small quantity of lime was added to the water so as to obtain a maximum pH of about 11.6. Moreover, the lime can be added from a silica—based and/or aluminium—based product.

The examples below illustrate these various improvements according to the invention.

Addition of lime a) To 158 kg of household refuse CV there was added 30 kg of water in which 0.03 kg of quicklime (CaO), that is to say 0.1%, had been dispersed. After the compacting operation a material with very good cohesion was obtained, the leaching results for which were as follows water/CV 0.19 pH Pb Cu Cd Zn Fe <0.4 <0.1 0.5 0.2 0.1 b) To 133.3 kg of household refuse CV there was added 30 kg of water in which 0.183 kg of CaO, that is to say 0.137%, had been dispersed. After compacting the mixture a material of cohesion superior to that of the product of experiment a) above was obtained and the leaching, moreover, was a bit less, for instance in the case of cadmium. initial pH Pb Cu Cd Zn Fe 0.1 water/CV .5 <0.4 <0.1 0.1 0.1 0.22 The compression—resistance of the material, after days, reached 7 megaPascal (MPa). c) In this example the lime introduced came from incineration smoke purification waste (DEF).

To 180 kg of household refuse CV there was added 50 kg of water in which was dispersed 7 kg of DEF (containing about 30.5% of lime, partly in carbonated form. A material of cohesion as good as that in example b) above, and with the following results for leaching (elements always expressed in ppm), was obtained. initial Pb Cu Cd Zn Fe Al water/ pH cv + DEF 7.6 0.3 Addition of a source of lime and silica To 100 kg of household refuse CV there were added 2 kg of CaO and 3 kg of carbon CV (as a source of silica), the latter two products being dispersed in 30 kg of water. The results after leaching were very good, as can be seen below initial Pb Cu Cd Zn Fe Al water/ pH CV+CaO + CV of carbon .3 0.1 Addition of a source of lime and aluminium To 158 kg of household refuse CV there was added kg of purification station waste water in which had been dispersed 8 kg of aluminous cement containing 38% of CaO and 39% of Algb. After the compacting operation the material had a good cohesion and an excellent The results after leaching resistance to compression. are summed up below initial Pb Cu Cd Zn Fe water/ pH CV and other 9 0.4 0.1 <0.l 0.1 0.1 0.18 In practice the addition of lime should be in a range of about 0.05 to 2 parts by weight per 100 parts by weight of CV to be treated.

As can be seen from the above examples the lime can be constituted by quicklime or slaked lime or even by any other source of lime such as aluminous cement, waste from acetylene manufacture, etc... The silica added can be fossil silica (diatomic earth), crushed silica, clay, loose carbon ash, crushed pozzuolana, asbestos waste, waste from ferrosilicon production etc.

As for the sources of aluminium they can also be in addition to aluminous various such as, for instance, cements, red muds used for the extraction of aluminium.

Claims (1)

1. Claims . Process for treating loose ash from household refuse incineration, excluding loose carbon ash, with a view to obtaining solid compositions resistant to a compression of up to 7 MPa, virtually insoluble in water and non—pollutant, characterised in that the ash is mixed with small quantities of water comprised between 10% and 35% of its weight and with small quantities of lime so as to bring the pH of the product obtained to a value of between 7.4 and ll.6, said obtained product then being compacted or extruded. . Process according to claim 1, characterised in that a part of the water is provided by sprinkling and the other part is added at the time of mixing or malaxation of the ash. Process according to any one of claims 1 or 2, characterised in that the water used comes from sources selected from the group; surface or underground water; waste water; mud from water- purifying stations; discharged leachates. . Process according to one of claims 1, 2 or 3, characterised in that the quantity of lime is from 0.05 to 2 parts per 100 parts (weight) of the ash. . Process according to one of the preceding claims, characterised in that the lime is associated with a 10 product including silica and/of aluminium. . Process according to claim 4, characterised in that the lime, silica and aluminium sources are selected from amongst products considered as waste, such as those from the manufacture of acetylene or ferrosilicon; red muds; smoke—purifying waste; and the like. F. R. KELLY & CO., AGENTS FOR THE APPLICANTS