A PROCESS AND APPARATUS FOR THE REMOVAL OF A CONTAMINANT FROM SLAG

Abstract: The present invention provides a decontamination process for the treatment of slag which includes the steps of pre-treating the contaminated slag with a process fluid containing at least one chemical; and subjecting the mixture of contaminated slag and process fluid to ultrasound. The present invention also provides an apparatus suitable for carrying out the process of the present invention.

Description: A PROCESS AND APPARATUS FOR THE REMOVAL OF A CONTAMINANT FROM SLAG The present invention relates to a process for the removal of a contaminant. In particular, the present invention relates a process for the removal of a contaminant from a by-product. More particularly, the present invention relates to a process for the removal of undesirable contaminants from slag produced during the smelting or refining of metals and like products. Additionally, the present invention provides an apparatus suitable for carrying out such process. During the smelting or refining of metals, a by-product molten material, commonly known as slag, is produced from the various input constituents in the furnace when it reaches 1400-1600°C. At present, the resultant slag is subsequently removed and quenched with water to produce a granulated solid material, which is then milled and classified. Millions of tons of slag are produced worldwide from a variety of metal production procedures, for example, iron, steel, copper etc. Whilst the resultant separated and classified slag has application in the production of cement, the amount of slag used in the overall percentage of cement has to be carefully controlled, since high levels of slag in cement results in a slower reaction time and moreover, the high calcium and magnesium levels found within such slags can cause swelling and distortion in the reacted cements. Therefore, it will be appreciated that only a relatively low amount of the slag produced can be utilised in downstream products, with the majority of the slag going to landfill as a co-disposal mechanism. In the particular case of blast furnace slag produced from steel production, the current method utilised to treat the slag for the removal of the undesirable contaminants therefrom, for example, calcium and magnesium, is to weather the slag in windrows that are periodically turned and managed for a period of up to one year. Such treatment is necessary before being able to utilise the treated or decontaminated slag in any substantial quantity. It will be appreciated that this current process of treating or decontaminating slag results in long periods before the treated slag can be utilised. Additionally, the current process requires high man time inputs and huge storage space requirements. Moreover, it will be appreciated that the weathering of slag in windrows can create highly undesirable run off waters as a result of the contaminants being washed from the slag over an extended period of time by rainfall, especially mildly acidic rainfall. As regards the by-products from, for example, zinc, lead and copper production, same cannot be treated as with steel slag and as such can pose a severe disposal problem and environmental hazard due to the very high levels of those metals as residues trapped within the stone or slag. Furthermore, there are high levels of valuable metals, which, if released, can be reclaimed for re-use. According to the present invention there is provided a decontamination process for the treatment of slag including the steps of pre-treating the contaminated slag with a process fluid containing at least one chemical; and subjecting the mixture of contaminated slag and process fluid to ultrasound. It is believed that a decontamination process in accordance with the present invention at least addresses the problems outlined above. In particular, the process in accordance with the present invention is able to handle the very large annual tonnage of slag produced as a by-product in the metal industry, it is energy efficient, it requires minimal man time input, it negates the contaminated run off water concerns and results in a decontaminated mineral or product that can be used in a wide range of important and value added applications, for example, in the production of acoustic panels, non-slip paints, fire retardant coatings, concrete block production etc. In addition, and in some instances, that is, depending on the constitution of the slag, the recovered or reclaimed metals can be used. In a further aspect of the present invention there is provided an apparatus for carrying out the decontamination process in accordance with the present invention the apparatus including: a first tank into which the slag and process fluids are added; at least one ultrasonic processor through which the slag and process fluids are passed; means for transporting the slag and process fluids from the first tank through the at least one ultrasonic processor and means for separating the process fluids from the decontaminated slag. One non-limiting embodiment of an apparatus suitable for carrying out the process of the present invention will now be described by way of example and with reference to the accompanying drawing in which: Figure 1 is a schematic illustration of a plant suitable for carrying out the process of the present invention. As illustrated, a plant in accordance with the present invention, includes a conveyor 10 to load the slag piles 20 into a pre-mix and treatment tank 11 , which contains a chemical mixture, the choice of which is directly dependent on the intended use of the processed slag and the resultant form of the slag, such as colour. In a preferred embodiment, the chemical mixture may include any one of the following, namely, hydrochloric acid, a surfactant, preferably an ionic surfactant, sulphuric acid, brine, carbon dioxide and depending on the desired colour, may also include hydrogen peroxide, acetic acid, ammonia etc. The resultant mixture of slag and desired chemicals are then transported from the pre-mix tank 11 to a series of ultrasonic processors 13. Preferably, such transportation is effected by the patented Tore ® system which is able to move very high-density materials, such as slag, with very high solid loadings, with high efficiency and low energy inputs. Once within the tubular ultrasonic processors 13, the mixture of slag and chemicals are subjected to a sonochemical reaction that results in the rapid dissolving and removal of the contaminant on the slag from both external and internal surfaces of the slag or base material. In this connection, the action of the ultrasound processors 13 forces the chemicals into the inner pore structure of the by-product materials, thereby enabling a deep decontamination to take place. An ultrasonic processor suitable for this application is disclosed in our European Patent Application No 96922160.5, the contents of which are incorporated herein by reference. The slag, which is now decontaminated, and the contaminant containing process chemicals or fluid is then passed over a dewatering screen 14, for example, a three deck separator sieve, whereby the now separate cleaned solids materials can be considered as ready for immediate use or may be size classified and dried depending on the chosen end use, for example, cement production, railway clinker, wall block production etc. The process chemicals, which result from the sonochemical process, after sieving, can then be recycled back into the pre-mix vessel 11 and the necessary chemical levels, for example, pH or alkalinity, can be monitored and maintained as required. In this connection, as the concentration of the removed contaminants increases to the point of precipitation, then the recycled fluids can be centrifuged to recover, for example, calcium chloride and magnesium chloride, which subsequent to being dried can be sold back into the chemical industry for use. In the case of the requirement for metal recovery from refining slags for either commercial or environmental reasons, a further step utilising an electrochemical process is required whereby levels of, for example, zinc, lead, nickel, chromium etc. have been removed up to a minimum of 99.5%. It is to be understood that the process and process plant of the present invention can be utilised to treat or decontaminate any type of slag or like product produced as a by-product during the smelting or refining or production of metals. In particular, it is to be understood that the process and apparatus in accordance with the present invention can be used to decontaminate any by-product of any metal production process.

Claims: CLAIMS 1. A decontamination process for the treatment of slag including the steps of pre-treating the contaminated slag with a process fluid containing at least one chemical; and subjecting the mixture of contaminated slag and process fluid to ultrasound. 2. The decontamination process of claim 1 , further including the step of separating the decontaminated slag from the process fluid. 3. The decontamination process of claim 2, wherein separation is effected via the use of a dewatering screen. 4. The decontamination process of any one of the preceding claims, wherein the process fluid includes at least one chemical selected from the group consisting of hydrochloric acid, a surfactant, sulphuric acid, brine, carbon dioxide, hydrogen peroxide, acetic acid and ammonia. 5. The decontamination process of any one of the preceding claims, further including the step of monitoring the pH of the process fluid. 6. The decontamination process of any one of the preceding claims, further including the step of treating the process fluids by centrifugation to recover a contaminant. 7. The decontamination process of claim 6, wherein the contaminant recovered is magnesium or calcium chloride. 8. The decontamination process of any one of the preceding claims, further including the step of treating the slag electro-chemically. 9. An apparatus for carrying out the decontamination process of any one of the preceding claims, the apparatus including: a first tank into which the slag and process fluids are added; at least one ultrasonic processor through which the slag and process fluids are passed; means for transporting the slag and process fluids from the first tank through the at least one ultrasonic processor; and means for separating the process fluids from the decontaminated slag.

Inventors: BALMER LESLIE WILLIAM, BALMER, LESLIE, WILLIAM
Applicants: BALMER LESLIE WILLIAM, NU ROCK SONICS LTD, BALMER, LESLIE, WILLIAM, NU-ROCK (SONICS) LIMITED
Application year: 2000
Main classification: C22B7
IPC codes: B09B5, C21B3, C21C1, C21C5, C21C7, C22B7