MXPA05001525A - Process and plant for converting hazardous waste containing chromium vi into non-hazardous waste - Google Patents

Abstract

The invention relates to a process und plant fur converting hazardous waste containing the contaminant chromium VI into non hazardous waste which can be stored without special precautions and which is broken down in the environment without time constraints. The inventive process essentially comprises:a grinding step;the extraction of the chromium VI in liquid phase under controlled agitation, time and temperature conditions;the conversion of the chromium VI into chromium III by means of reduction;and subsequently, the precipitation thereof as chromium trioxide by means of gasification. The solid resulting from the conversion process can be used as a raw material for the construction of fire bricks or optionally for the production of partitions used in construction using a process that is not included in the description.

Description

PROCESS AND PLANT FOR THE TRANSFORMATION OF HAZARDOUS WASTE WITH CHROMIUM SIX CONTENT IN WASTE NO DANGEROUS TECHNICAL FIELD OF THE INVENTION The present invention is directed to the industrial processes of leaching of chemical and mineral components derived from toxic waste and its subsequent treatment for the transformation of hazardous waste with chromium content six into non-hazardous waste or pollutants and / or used for the manufacture of articles for construction. The invention is also related to the branch of mining and its industrial products of waste of high economic value derived from the processes inherent to the metallurgical industry.

BACKGROUND OF THE INVENTION The present invention relates to a new process and its relative plant for the transformation of. hazardous waste with chromium content six (CR + D), in non-hazardous waste that comply with the CRETIB analysis. The process comprises the steps of milling, water suspension, partial recovery of the six chromium present, chemical treatment for the reduction of all the chromium six present to chromium three by the action of a sulfur gas anhydride mixture with residual sulfuric acid from the manufacture of liquid vaselines, basification. Finally, the resulting product, once the CRETIB analysis has been completed, can be used as a raw material for the manufacture of refractory bricks or, failing that, to store it without any special requirement because it is a non-hazardous waste. The aforementioned hazardous waste originates mainly in the production of sodium bichromate by alkaline melting of chromium ore in an oxidizing atmosphere in different types of kilns according to the applied process, extracting in a second stage, by leaching a chromate solution of Sodium, which is acidified by sodium bichromate, resulting in byproducts of alumina or aluminum hydroxide contaminated with variable amounts of chromium six, which together with the final residues of leaching are hazardous waste, in the case of sulphate sodium, it is feasible, its recrystallization, for its purification, to be used as a raw material in the paper industry or in various chemical processes. In the case of contaminated alumina and the leaching residue, they constitute hazardous waste, as already mentioned. The residue of leaching is constituted by insoluble chromates, iron salts, complex silicates that include chromium in their composition, in addition chromium salts encapsulated by the silicates and insoluble salts, which hinders their reduction and / or extraction, so that the present invention is directed to eliminate these barriers and achieve 100% effectiveness in the reduction processes, verified through compliance with the CRETIB analysis. That is why the documents of the state of the art related to the present invention are mentioned below, which are mentioned below with the purpose of including them only as references. There is an antecedent in the Patent Application MX No. 9300307 filed on January 21, 1993 by Luigi Stoppani SPA, which is based on a treatment at a temperature of 450 degrees centigrade with sulfur in an atmosphere with low oxygen content, in a tubular furnace closed at its ends and with indirect heating, the advantage of the present invention, is that it is not necessary to use a complicated installation and process as described in the aforementioned patent application, as mentioned previously used grinding and suspension in water, a reductive mixture of sulfur dioxide and residual sulfuric acid from the production of vaselines in stirred reactors without the need for heating or isolating the system from the atmosphere, does not influence the reaction, it's a batch process, but continuous flow because a minimum of three reactors are used, the total reduction is assured by the CRETIB analysis, the resulting material is usable in the fabrication of refractory bricks or partitions, thus obtaining a full use of the mineral resources present In nature. The process described in the present invention and the Stoppani process are two very different processes. The Stoppani process is developed in a closed furnace by a solid gas reaction, where the control of the reaction and its efficiency are not clearly disclosed and is confused by the reading of the patent document. In the process of the present invention, the reaction is carried out in a liquid medium in a reactor, where previously an extraction of the chromium to be reduced takes place and then the chemical reaction, acidification and subsequent reduction are carried out in a perfectly homogeneous phase, verifiable complete stabilization through the CRETIB analysis, which does not occur in the Stoppani process. However, in the process of the invention, the control of the efficiency is perfectly traceable and verifiable at any time of the process. Reiterating, the purpose of the present invention is to obtain the protection scope justified and validated by the detailed description that is mentioned below and by the technical-scientific development invested in the investigations of the described examples, and against a possible protection granted to third parties, this by virtue of the fact that the state of the art previously mentioned does not totally eliminate chromium six and confines it as hazardous waste.

OBJECTIVES AND ADVANTAGES OF THE INVENTION In general, and based on the background described above in relation to the processes for the transformation of hazardous waste with chromium six content into non-hazardous waste, it can be interpreted that there are still no highly effective processes for the long-term disposal of hazardous waste. In this context, then, the justification of the current need to develop new technologies or processes for the transformation of such waste is obvious. Accordingly, the present invention has the following objects. The main object of the present invention is directed to a process and its related plant for the extraction and reduction of chromium six compounds present in hazardous waste, under the forms of chromium compounds of low solubility or encapsulated within insoluble compounds. In addition, another objective of this invention is to reveal the process of transformation of hazardous waste, which begins with a milling, washing, suspension in water, treatment with a mixture of residual sulfuric acid from the manufacture of liquid petrolatum and sulfur dioxide, fulfilled the total reduction, is basified to pH 8- 8.5. Finally, another objective of the present invention is to use the material resulting from the process of the invention for the manufacture of partitions and refractory bricks, as it does not constitute a hazardous waste. Thus, as in the present invention, the process for the transformation of hazardous waste containing chromium six into non-hazardous waste is disclosed.

BRIEF DESCRIPTION OF THE FIGURES Other features and advantages of the invention will be apparent from the following detailed description, of the objectives and preferred embodiments, of the appended claims and of the accompanying figure, wherein: Figure 1 shows a process flow diagram and plant for the transformation of hazardous waste with chromium content six into non-hazardous waste of the invention.

DETAILED DESCRIPTION OF THE INVENTION The process object of the present invention comprises the steps of: a) a transport of the hazardous waste with chromium content six to be treated, to the Process Plant, being the first unit operation; b) a first grinding through a broken jaw, to reduce the larger pieces that are formed during the storage of the waste to particles no larger than an inch in diameter, and then complete with c) a second grinding in a mill to balls, having to obtain a powder with a granulometry in which 80% passes through a 200 mesh screen, is then carried out d) a first wash with water to extract the six chromium in liquid phase and its soluble salts, the resulting diluted solution is sent to the process of obtaining sodium bichromate as process waters; e) unload the ground material, fulfilling the specified granulometry and having it subjected to a first washing, to a conveyor belt, which transfers it to a silo, which feeds the reactors where the complete reduction of chromium six is carried out, remnant of the first washed. As mentioned, the stainless steel reactors of twenty thousand liters of capacity are fed with water in the same mass as the waste to be charged; f) add the waste from the feeder silo, always with the agitator in functioning; g) add the residual sulfuric acid from the manufacture of liquid vaselines gradually, since the neutralization and reduction process is strongly exothermic; h) maintain that the temperature does not exceed 80 ° C; the amount of residual sulfuric acid is dosed; i) control the pH of the suspension to a value of 2.5 +/- 0.5; j) stirring for half an hour and then a gaseous stream of reducing agent is injected from the bottom, maintaining the stirring depending on the time and the amount to be injected of the present percentage of chromium six; and k) perform a determination of chromium six, whose value must be zero and subsequently basify to a pH of 8-8.5, extract a new sample and submit to the analysis called CRETIB. (Corrosive, reactive, explosive, toxic, flammable, biological infectious). Once the aforementioned CRETIB analysis has been carried out, it is discharged to separate the process water from the non-hazardous waste obtained, this operation can be done by simple decanting in storage cells or using filters whose design and capacity depends on the volumes to be processed daily. The material obtained, as already specified, is suitable to be used as raw material for the manufacture of partitions and / or refractory bricks, whose feasibility was proven through numerous experiences, studies and Applications . In the description of the flow diagram of Figure 1, the hazardous waste with content of chromium six is transported to the reception hopper (1), which feeds the conveyor belt (2), which leads the material to the breaker of hammers (3), this reduces the granulometry to pieces of maximum one inch in diameter, the material is sent by the bucket elevator (4) to the vibrating screen (5), which feeds the storage silo (6), this in turn feeds the ball mill (7), where a wet milling is carried out so that 80% passes through a 200 mesh screen, the material is classified in the cyclone (8), the finest material passes to the agitator tank (9), where the suspension of the 50% material is carried out in water, the thicker material separated in the cyclone returns to the ball mill of the agitator tank (9), the suspension is transferred to the reaction reactors (10), where they are acidified with residual sulfuric acid or sulfuric acid 98% until the pH is reduced to 2.5-3, a gaseous stream of reducing agent is injected maintaining the temperature at 80 ° C with continuous stirring for four hours, a sample is taken and the concentration of chromium six is determined, which must be below 0.5 ppm by spectrophotometry, the pH is modified again to 8.5-9, another sample is taken for final analysis of CRETIB, it is discharged to the evaporation pit (11) and final disposal for the manufacture of partitions and refractory bricks. The present invention relates to a novel process for the transformation of hazardous waste with chromium six content as a contaminant in non-hazardous waste that can be stored without special care and will be degraded in the environment without time limits. The process basically consists of a grinding, extraction of chromium six in liquid phase and under controlled conditions of agitation, time and temperature, to subsequently proceed by reduction, transform chromium six into three chromium and its subsequent precipitation as chromium trioxide, by basification . The solid resulting from the transformation process can be used as raw material for the construction of refractory bricks or eventually for the manufacture of partitions used in the construction by a process that is not included in the present description. In addition, the present invention provides a novel process for the efficiency achieved through its application, since a hazardous waste with variable content of chromium six is transformed into a non-hazardous waste by eliminating all chromium six until it complies with environmental legislation as opposed to the applied processes normally in the industry where the presence of chromium six is reduced by different techniques, but they continue in the classification of hazardous waste, which must be stored in very strict conditions of isolation and control with the possibility of filtering as a function of time since No one can guarantee the safety of no accidental contamination in a period greater than one hundred years. The final product obtained by the process object of this invention not being a hazardous material there is no possibility of contamination in the present or the distant future. The process of the present invention begins with a two-stage milling, first by breaking mandibles, reducing its size to particles of maximum one inch, then passing by conveyor belt to a ball mill, which reduces the granulometry so that pass 80% through a 200 mesh sieve. By means of a bucket elevator it is conducted to a storage silo of ground material from which the reaction reactors are fed, where a fifty percent suspension is produced in water and then added to Graduated form diluted sulfuric acid, which can be residual of another industrial process until reducing the pH of the suspension up to 2.5-3, the neutralization reaction is exothermic and must be controlled at 80 ° C and keep it at that value with continuous agitation for four hours, and under optimum temperature and residence time according to the graphs opportunely made of temperature efficiency against time. After the established reaction times have elapsed, a representative sample of the suspension is taken and the CRETIB analysis described in additional form is carried out. If the concentration of chromium six present is less than 0.5 ppm, pumping is carried out to the jale dam where the process solution is separated from the solid material, which can be stored in the jail dam using the cell method, which are closed once filled to cover them with earth "lama" for later to plant native flora or also as an option you can use the solid obtained as raw material for the manufacture of refractory bricks or partitions for the construction The previous description and the following examples have as a purpose to illustrate particular ways of carrying out the invention and should not be considered as limiting the scope of protection thereof.

EXAMPLES The process is applied for the reduction of chromium six, present in the waste coming from the production of sodium bichromate.

The manufacture of sodium bichromate is obtained by an alkaline melting at 1200 ° C in an oxidizing atmosphere inside a rotary kiln with a controlled residence time, then the sodium chromate formed by leaching with water is extracted, this solution is submitted at a concentration, pH reduction and purification to finally obtain the sodium bichromate in solution or in crystals. After leaching, a mixture of salts and silicates of iron, calcium, sodium and chromium is left as hazardous waste in percentages that depend on the characteristics of the applied process, but that normally exceed 2%, being the limit to be considered a waste not dangerous 0.5 ppm. All companies apply a primary process that reduces the content of chromium six, but does not reach 0.5 ppm. In our case, the novelty is that after being treated, the waste meets the aforementioned maximum limit of 0.5 ppm of chromium six, which is verified through the CRETIB analysis, resulting in a non-hazardous waste, which is stored under normal conditions, no need for any special care for having returned the chromium to its state in nature, that is, to chrome three.

STABILIZATION PROCESS The process begins with a grinding of the waste, To facilitate the reduction reaction completely, for the reason that chromium is encapsulated inside complex silicates, which are what prevent a complete stabilization of the chromium six present, this being a fundamental stage for achieving compliance with the characteristics of non-hazardous waste. After grinding, the residue is suspended in water and treated with sulfuric acid to reduce the pH to 2-2.5, a necessary condition for the reduction of chromium six. All this under controlled temperature conditions. Subsequently, a gaseous stream of sulfur dioxide, which is the reducing agent, is injected, also under controlled conditions of temperature and agitation. The CRETIB analysis is carried out, if it is carried out it is sent to the definitive warehouse. For this, a process plant was designed, which was also approved and authorized by the National Institute of Ecology together with the process.

CRETIB ANALYSIS Its name means that a waste not to be considered dangerous, must not be corrosive, reactive, explosive, toxic, flammable and biological infectious. The specific procedure for the residue of the present invention consists of taking a sample representative, divide it into four, place it in a team, consisting of four closed tubes of 500 milliliters, with water and subject the test tubes to an oscillatory movement for 24 hours, in order to extract all the soluble chromium, which then determines its concentration by spectrophotometry and in particular it should not be higher than 0.5 ppm.

EXAMPLE OF OPERATION The residue is milled until 80% passes through mesh 200, a reactor is loaded with 5000Kg on the same amount of water, sulfuric acid is added until the suspension has a stable pH of 2.5-3, a reducing agent selected from the group consisting of ferrous salts and sulphurous anhydride is added, failing that, sulfur dioxide, stirring for four hours and maintaining a temperature of 80 ° C, which is originally reached without heating because of the dilution of sulfuric acid in water, in an exothermic reaction. After a period of four hours, a sample is taken, the concentration of chromium six in the solution is determined and if it is below 0.5 ppm, the pH is raised with sodium hydroxide solution to a pH value 8.5-9 to precipitate all three chromium salts formed as insoluble chromium tritoxide, proceed in that moment to the pumping of the suspension to a storage type dam of jale where quickly the separation of the solid of the supernatant liquid takes place, which is returned to the process to be used again as an extraction liquid mixing it in equal parts with fresh water.

DESCRIPTION OF THE PLANT The hazardous waste treatment plant with chromium content consists of the following areas: Grinding 1 ° The material is transported by dump trucks to the area of entry to the process, which is the milling area, a vibrating hopper is fed, which feeds a jaw breaker that reduces the granulometry of the waste to pieces no larger than one inch. 2 ° The material from the crusher feeds a conveyor belt that leads to the second stage of grinding, a ball mill, which reduces the granulometry so that 80% passes through a 200 mesh screen, this with the purpose of exposing all chromium derivatives six to the extraction and reduction process. 3 o The ground material is sent to a storage silo by means of a bucket elevator. The entire grinding stage has aspiration of powders and cyclones, and bag filters for the control of emissions.

Chemical Reaction Three stainless steel reactors are used ,000 liter each with agitation and heating by steam chamfering, extraction and washing of gases, injecting pipe of a gas stream of sulfur dioxide, temperature control, dosing pumps for the addition of diluted sulfuric acid and, if necessary, of the additional reducing agent used . The operation of the reactors is by batch, but sequentially the three reactors so that the process itself has the continuous character.

Storage of Raw Materials Will have: Io A carbon steel tank of 20,000 liters of minimum capacity for the storage of sulfuric acid. 2 ° A carbon steel tank of 20,000 liters of minimum capacity for the storage of the alternative auxiliary reducing agent. 3 ° A battery of four cylinders of liquid sulfur dioxide of 1000 Kg each and / or a connection by means of suitable pipe to a continuous generating plant of a stream of 8% sulfur dioxide in air.

Storage of the Final Product The treated material or hazardous waste transformed into non-hazardous material will be stored in a jale-type reservoir, where the separation of the solutions resulting from the process and the solid to be stored takes place, the size of this warehouse logically depends on the mass to be treated, being able to build modular cells, which once filled to their maximum capacity are closed and covered with organic earth, to plant native flora. The entire plant, including areas or areas of temporary storage, must comply with safety and ecological regulations. It should be apparent to those skilled in the art that other variations not specifically disclosed in the present invention, but which, however, are proposed by the present detailed description and are considered to fall within the scope of protection of this invention. . Therefore, the invention should not be limited by the description of the specific embodiments disclosed, but only by the following claims.

Claims (17)

1. A process for the transformation of hazardous waste with content of chromium six into non-hazardous waste, characterized in that said process comprises the steps of: a) transportation of the hazardous waste with chromium content six to the process plant; b) a first grinding through a broken jaw, to reduce the larger pieces that are formed during storage of the waste to particles no larger than one inch in diameter; c) a second grinding in a ball mill, obtaining a powder with a granulometry in which 80% passes through a 200 mesh screen; d) a first wash with water to extract chromium six in liquid phase and its soluble salts, the resulting diluted solution is sent to the process of obtaining sodium bichromate as process waters; e) unload the ground material, fulfilling the specified granulometry and having it subjected to a first washing, to a conveyor belt, which transfers it to a silo, which feeds the reactors where the complete reduction of chromium six is carried out, remaining of the first wash; f) add the waste from the feeder silo, always with the agitator in operation; g) add the residual sulfuric acid from the manufacture of liquid vaselines gradually, since the neutralization and reduction process is strongly exothermic; h) maintain that the temperature does not exceed 80 ° C; i) control the pH of the suspension to a value of 2.5 +/- 0.5; j) stirring for half an hour and then a gaseous stream of reducing agent is injected from the bottom, maintaining the stirring depending on the time and the amount to be injected of the present percentage of chromium six; and k) perform a determination of chromium six, whose value must be zero and subsequently basify to a pH of 8-8.5, extract a new sample and undergo the analysis called CRETIB.

2. The process according to claim 1, characterized in that it also comprises discharging the ground material to separate the process water from the non-hazardous waste by decanting into storage cells or using filters.

3. The process according to claim 1, characterized in that it further comprises transforming chromium six into three chromium and its subsequent precipitation as chromium tritoxide, by gasification.

4. The ground material obtained by the process according to claim 1, which is used as a raw material for the manufacture of partitions and / or refractory bricks.

5. The process according to claim 1, characterized in that said process comprises: the hazardous waste with content of chromium six is transported to the reception hopper (1), which feeds the conveyor belt (2), which leads the material to The hammer crusher (3), this reduces the granulometry to pieces of maximum one inch in diameter, the material is sent by the bucket elevator (4) to the vibrating screen (5), which feeds the storage silo (6). ), this in turn feeds the ball mill (7), where wet milling is carried out so that 80% passes through a 200 mesh screen, the material is classified in the cyclone (8), the finest material passes to the agitator tank (9), where the material is suspended at 50% in water, the thicker material separated in the cyclone returns to the ball mill of the agitator tank (9), the suspension is transferred to reaction reactors (10), where they are acidified with residual sulfuric acid or 98% sulfuric acid until the pH is reduced to 2.5-3, a gaseous stream of reducing agent is injected maintaining the temperature at 80 ° C with continuous agitation for four hours, a sample is taken and the concentration of chromium six is determined, which must be below 0.5 ppm by spectrophotometry, the pH is modified again to 8.5-9, another sample is taken for final analysis of CRETIB, it is discharged to the evaporation pit (11) and final disposal for the manufacture of partitions and refractory bricks.

6. The process according to claim 5, characterized in that if the concentration of chromium six present is less than 0.5 ppm, pumping is carried out to the pull dam where the process solution is separated from the solid material, which can be stored in the jale dam using the cells procedure, which are closed once filled to cover them with earth lama and then plant native flora or also as an option you can use the solid obtained as raw material for the manufacture of refractory bricks or partitions for the built

. The process according to claim 1 or 5, characterized in that the process is applied for the reduction of chromium six, present in the residues from the production of sodium bichromate.

8. The process according to claim 7, characterized in that the sodium bichromate is obtained by an alkaline melting at 1200 ° C in an oxidizing atmosphere inside a rotary kiln with a controlled residence time, then the sodium chromate formed by leaching with water, this solution is subjected to a concentration, pH reduction and purification to finally obtain the sodium bichromate in solution or in crystals.

9. The process according to claim 8, characterized in that, after leaching, a mixture of salts and silicates of iron, calcium, sodium and chromium six remains as a hazardous waste in percentages normally exceeding 2%, the limit being considered a non-hazardous waste 0.5 ppm.

10. The process according to claim 9, characterized in that after being treated the waste complies with said maximum limit of 0.5 ppm of chromium six, which is verified through the CRETIB analysis, resulting in a non-hazardous waste, which is stored in normal conditions, without any special care for having returned the chromium to its state in nature, that is, to chrome three.

11. The process according to claim 1 or 5, characterized in that the milling step of the waste facilitates the reduction reaction in complete form, for the reason that the chromium is encapsulated within complex silicates.

12. The process according to claim 1 or 5, characterized in that the reducing agent is selected from the group consisting of ferrous salts and sulfur dioxide.

13. The process according to claim 1 or 5, characterized in that after a period of time of four hours, a sample is taken, the concentration of chromium six in the solution is determined and if it is below 0.5 ppm, it rises the pH with sodium hydroxide solution up to a value of pH 8.5-9 to precipitate all the chromium salts three formed as insoluble chromium tritoxide, proceeds at that moment to the pumping of the suspension until a storage type dam jale where quickly produces the separation of the solid from the supernatant liquid, which is returned to the process to be again used as extraction liquid mixing it in equal parts with fresh water.

14. A plant for the transformation of hazardous waste with content of chromium six into non-hazardous waste, characterized in that said plant includes: a grinding area, where the material is transported by dump trucks to the area of entry to the process; a vibratory hopper, which feeds a jaw crusher that reduces the granulometry of the residue to pieces no larger than one inch; a conveyor belt, which drives the material from the crusher to the second stage of milling; a ball mill, which reduces the granulometry so that 80% passes through a 200 mesh screen, this in order to expose all the chromium derivatives six to the extraction and reduction process; a storage silo, where the ground material is sent by means of a bucket elevator; a chemical reaction area, where three stainless steel reactors of 20,000 liter each are used, with agitation and heating by steam chacking, extraction and washing of gases; an injection pipe of a gaseous stream of sulfur anhydride; a temperature control; dosing pumps for the addition of dilute sulfuric acid and, if necessary, the additional reducing agent used; a carbon steel tank of 20,000 liters of minimum capacity for the storage of sulfuric acid; a carbon steel tank of 20,000 liters of minimum capacity for the storage of the alternative auxiliary reducing agent; a four-cylinder battery of liquid sulfur dioxide of 1000 kg each; and / or a connection by means of suitable pipe to a continuous plant generating an 8% sulphurous anhydride stream in air; and a jale type deposit, for the storage of the treated material or hazardous waste transformed into non-hazardous, where the separation of the solutions resulting from the process and the solid to be stored takes place.

15. The plant for the transformation of hazardous waste with chromium content six into non-hazardous waste according to claim 14, characterized in that the grinding area has aspiration of dust and cyclones, and bag filters to control emissions.

16. The plant for the transformation of hazardous waste with content of chromium six into non-hazardous waste according to claim 14, characterized in that the three reactors operate sequentially by batch, so that the process is continuous.

17. The plant for the transformation of hazardous waste with content of chromium six into non-hazardous waste according to claim 14, characterized in that the size of the reservoir type dam jale depends on the mass to be treated, being able to build modular cells, which Once full to their maximum capacity they are closed and covered with organic earth, to plant native flora.