DESC:*** Complete Specification ***

“Method to obtain mineralizer and fuel from spent potline waste using dolomite at preheating stage”

Cross references to related applications: This complete specification is filed further to patent application No. 202331056646 dated 24/02/2024 and the entire content of the provisional specification filed therewith is incorporated herein in its entirety by way of reference.

Field of the invention
This invention belongs to the aluminum industry and relates therein generally to the utilization of waste materials, especially hazardous wastes generated during aluminum production. Specifically, the disclosures hereunder are directed to a process for treating SPL for obtaining value added products which can be used as fuel or mineralizer to steel, cement and ferroalloys industries.

Definitions and interpretations
Before undertaking the detailed description of the invention below, it may be advantageous to set forth definitions of certain words or phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect, with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and certain definitions are set forth for this document, as follows: -
(a) “SPL” shall refer Spent Pot Lining.

Background of the invention
SPL is a hazardous waste generated from the aluminum smelting process, specifically from the cathode lining of electrolytic cells (pots). Also, as an effect of long-term operation of the aluminum electrolysis (Hall-Heroult) cells, various molten salts continuously infiltrate and corrode the pot lining, resulting in a copious accumulation of hazardous wastes. Eventually, the pot lining gradually expands and ruptures, resulting in numerous irregular working conditions.

SPL contains a mixture of carbon, refractory materials, and various toxic compounds, posing significant environmental and health risks, such as:
(a) Toxic Leachate: SPL contains fluoride, cyanide, and heavy metals, which can leach into groundwater and contaminate drinking water sources.
(b) Air Pollution: Improper disposal or incineration can release toxic gases like hydrogen fluoride (HF), ammonia (NH3), and cyanide, affecting air quality.
(c) Soil Contamination: If dumped in landfills, the toxic components can degrade soil quality and affect plant and microbial life.
(d) Water Pollution: Rainwater can carry dissolved contaminants from SPL into nearby water bodies, harming aquatic ecosystems.
(e) Respiratory Issues: Exposure to dust and gases from SPL, especially fluoride and cyanide, can cause respiratory problems and lung damage.
(f) Skin and Eye Irritation: Direct contact with SPL can cause burns, irritation, and allergic reactions.
(g) Neurological Effects: Chronic exposure to cyanide and fluoride can lead to nervous system damage, cognitive impairment, and other neurological disorders.
(h) Carcinogenic Potential: Some components of SPL, such as polycyclic aromatic hydrocarbons (PAHs), are known to have carcinogenic properties.
(i) Fire and Explosion Hazards: The carbonaceous material in SPL can react with moisture to generate flammable gases like acetylene and hydrogen, posing fire and explosion risks.
(j) Corrosive Nature: Fluoride and sodium compounds in SPL can corrode equipment, leading to operational hazards in industrial settings.

The formation rate of SPL is around 25 kg per ton of primary aluminum production, and about 1.7 million tons of SPL are generated each year worldwide (B.I. Silveira et al. Characterization of inorganic fraction of spent potliners: evaluation of the cyanides and fluorides content; J. Hazard. Mater. (2002)).

Therefore, due to its hazardous nature, SPL disposal needs to be strictly regulated, and improper handling can result in legal and financial liabilities for industries. Hence, regular removal of SPL is a requisite in aluminum production processes the world over, resulting in large quantities of SPL being generated.

Description of related art
Disposal of SPL, done conventionally in landfills, has a deeply negative environmental impact, and hence subject of grave concern, therefore a severe challenge to the aluminum industry. Therefore, it would be very desirable to have some effective means for harmless disposal and / or resource utilization of SPL.

Numerous methods have been tried to detoxify and purify SPL, such as water washing, flotation, chemical leaching, and thermal treatment. However so far, the traditional utilization strategies, SPL is mainly used as an energy material with coal, fluxing agent in cement production, and carbonaceous additive in the electrolysis process (K. Yang et al. Graphitic carbon materials extracted from spent carbon cathode of aluminium reduction cell as anodes for lithium ion batteries: converting the hazardous wastes into value-added materials; J. Taiwan Inst. Chem. Eng.(2019)). Therefore there is a pressing need in art to broaden the perspective of resource utilization of SPL.

Prior art, to the extent surveyed, lists some scattered attempts to address the issues mentioned hereinabove. For example, US4735784A (Filed 1986, Assigned to Morrison Knudsen Co Inc) teaches a method of treating fluoride contaminated wastes by adding silica, elevating the temperature of said mixture within the range of 1,000° to 1,700° C. to form a slag; providing sufficient silica in the mixture and forming the slag in the presence of sufficient water for pyrohydrolysis conditions resulting in the volatilization of substantially all of the fluoride contaminants mostly in the form of hydrogen fluoride; and cooling the slag remaining after volatilization of substantially all of the fluoride contaminants to produce an insoluble silicate glass-residue containing any remaining portion of the fluoride contaminants in an immobile state.

Another example is WO2011040988A1 (Filed 2010, Filed by Mark Weaver et al) teaches a method for treatment of bauxite residue and spent pot lining, The treatment processes are capable of producing a ferrosilicon alloy, an off-gas, and/or a byproduct material resulting in the safe disposal of SPL and bauxite residue. The treatment processes may be continuously carried out in an electric arc furnace at a temperature in the range of from about 1500°C to about 2200°C and for a period of from about 15 to about 100 minutes.

The above solutions, though promising, are not ideal, due to the persistence of at least the following technical issues-
(a) Chemical and Physical Challenges:
a. High Toxicity of SPL: SPL contains cyanides, fluorides, and heavy metals, which pose serious environmental and health risks, and thus requires specialized treatment to neutralize these toxic components before disposal.
b. Reactivity with Moisture: SPL reacts with water to generate flammable and toxic gases like hydrogen (H2), acetylene (C2H2), and ammonia (NH3), and thus can cause explosions or uncontrolled gas emissions if not handled properly.
c. Variability in Composition: The chemical makeup of SPL varies depending on the aluminum smelting process and pot design. This inconsistency makes standardization of treatment processes difficult.
(b) Processing and Treatment Issues:
a. Challenges in Co-Processing in Cement Kilns: Requires precise blending to avoid adverse effects on cement quality. Fluoride emissions must be controlled to prevent damage to kiln refractory linings. Not all cement plants are equipped to handle hazardous waste.
b. Difficulties in Vitrification (Glassification): High energy consumption and operational costs. Fluorides and cyanides may volatilize during melting, requiring advanced gas scrubbing systems.
(c) Problems in Chemical Treatment and Neutralization: Chemical treatment generates secondary waste that needs further disposal. Neutralization processes must be carefully controlled to avoid incomplete detoxification.
(d) Secure Landfilling Limitations: SPL requires engineered hazardous waste landfills with double liners and leachate treatment systems. Long-term monitoring is essential to prevent groundwater contamination. Limited landfill space and high disposal costs make this option unsustainable.
(e) Operational and Economic Constraints:
a. High Treatment and Disposal Costs: Technologies like vitrification and chemical treatment require significant capital investment. Landfilling and co-processing require compliance with strict environmental regulations, increasing costs.
b. Limited Infrastructure for SPL Recycling: SPL recycling into cement, steel, and other industries is still in early stages. Many industries lack the technology or willingness to invest in SPL recovery.
(f) Transportation and Storage Risks: SPL must be stored and transported in sealed, moisture-free conditions to prevent hazardous reactions. Specialized handling procedures increase logistical costs.

State-of-art therefore, does not list a single effective solution embracing all considerations mentioned hereinabove, thus preserving an acute necessity-to-invent for the present inventor/s who, as result of focused research, has come up with novel solutions for resolving all needs once and for all. Work of the applicant/s hereof, specifically directed against the technical problems recited hereinabove and currently part of the public domain including earlier filed patent applications, is neither expressly nor impliedly admitted as prior art against the present disclosures.

A better understanding of the objects, advantages, features, properties and relationships of the present invention will be obtained from the following detailed description which sets forth an illustrative yet-preferred embodiment.

Objectives of the present invention
The present invention is identified in addressing at least all major deficiencies of art discussed in the foregoing section by effectively addressing the objectives stated under, of which:

It is a primary objective to provide

It is another objective further to the aforesaid objective(s) that

The manner in which the above objectives are achieved, together with other objects and advantages which will become subsequently apparent, reside in the detailed description set forth below in reference to the accompanying drawings and furthermore specifically outlined in the independent claims. Other advantageous embodiments of the invention are specified in the dependent claims.

Brief description of drawings
The present invention is explained herein under with reference to the following drawings, in which:

FIG. 1 is a flow chart illustrating the process flow / logic of the present invention.

The above drawings are illustrative of particular examples of the present invention but are not intended to limit the scope thereof. The drawings are not to scale (unless so stated) and are intended for use solely in conjunction with their explanations in the following detailed description.

Attention of the reader is now requested to the detailed description to follow which narrates a preferred embodiment of the present invention and such other ways in which principles of the invention may be employed without parting from the essence of the invention claimed herein.

Statement / Summary of the invention
The present invention provides a novel method for treating SPL through a sequence of controlled chemical and thermal processes. The method effectively neutralizes hazardous components, particularly fluoride and cyanide compounds, while producing value-added products. The primary steps of the process involve (a) Treatment with Calcined Dolomite; and (b) Heat Treatment.

Detailed description
The present invention relates to a standardized process for the treatment of Spent Pot Lining (SPL), an industrial waste generated from aluminum production. More specifically, it pertains to an improved method that absorbs the advantages of prior art while eliminating any drawbacks, thereby facilitating the safe and efficient transformation of SPL into value-added products suitable for use as fuel or mineralizers in the steel, cement, and ferroalloy industries.

The applicant herein has explored the possibility of salvaging products of potential economic value from SPL.

Attention of the reader is now requested to the brief description to follow which narrates a preferred embodiment of the present invention and such other ways in which principles of the invention may be employed without parting from the essence of the invention claimed herein

Accordingly, the preferred embodiment of the present invention as illustrated in FIG. 1 is identified in the performance of the following sequence of steps-

Step 1: Treatment with Calcined Dolomite
SPL is first mixed with 15% calcined dolomite fines of size up to 1mm size with retention period of 24 hours, which serves a dual purpose of eliminating moisture and binding fluoride compounds into stable, non-leachable forms. The primary chemical reactions governing this step are:

2NaF + CaO.MgO ? CaF2 + MgO + Na2O …………… (a)

2NaF + CaO.MgO ? CaF2 + MgF2 + Na2O …………… (b)

In these reactions, Sodium fluoride (NaF), a soluble and hazardous compound, reacts with calcium and magnesium oxides in calcined dolomite. The resulting calcium fluoride (CaF2) and magnesium fluoride (MgF2) are stable, insoluble compounds that do not leach into water sources. Sodium oxide (Na2O) is formed as a by-product, which can further contribute to the mineralization process in subsequent applications. This step ensures complete fixation of fluoride ions, preventing them from contaminating groundwater or runoff.

Step 2: Heat Treatment
After treatment with calcined dolomite, the mixture is subjected to a controlled heating process in ribbon blender at 500oC. This step serves two critical functions:
(a) Breaking Down Cyanides: Cyanide compounds present in SPL, particularly sodium cyanide (NaCN), are decomposed into non-toxic forms under oxidizing conditions.
(b) Preventing Fluoride Emissions: The presence of calcined dolomite in the mixture ensures that fluorides remain bound in stable mineral forms even at elevated temperatures.

The heating process is carefully optimized to maximize safety, ensuring that no hazardous gases are released into the atmosphere.

Step 3: Final Product Utilization (Industrial utility)
The treated SPL material is transformed into a non-toxic, stable product with high utility in industrial applications, including:
(a) Steel Industry: Used as a fuel or fluxing agent in steel manufacturing.
(b) Cement Industry: Enhances clinker formation and mineralization in cement production.
(c) Ferroalloys Industry: Contributes to alloy formulation by acting as a mineralizing agent.

Equipment for treating SPL waste via implementing the process methodology above comprises-
(a) A reaction chamber for mixing SPL with calcined dolomite and thereby facilitating the controlled hydration of calcined dolomite to absorb moisture and bind fluorides;
(b) A heat treatment unit for breaking down cyanides, said unit being designed to operate at a temperature sufficient to prevent atmospheric escape of hazardous fluorides;
(c) A collection system for the final treated product, which can be used in steel, cement, and ferroalloy industries.

This invention effectively turns a hazardous waste material (SPL) into a valuable resource, offering both environmental and economic benefits, including-
(a) Environmental Safety: Eliminates leachable fluorides and cyanides, preventing water and air pollution.
(b) Value Addition: Converts SPL into a useful material, reducing waste disposal costs and creating new economic opportunities.
(c) Process Efficiency: Provides a streamlined, scalable approach suitable for industrial adoption.
(d) Regulatory Compliance: Ensures adherence to environmental standards for hazardous waste management.

Therefore, the present invention introduces a robust and effective method for treating SPL, transforming it into safe, industrially beneficial products. By leveraging chemical and thermal treatment, this process not only neutralizes hazardous components but also enhances sustainability across multiple industries.

As will be realized further, the present invention is capable of various other embodiments and that its several components and related details are capable of various alterations, all without departing from the basic concept of the present invention. Accordingly, the foregoing description will be regarded as illustrative in nature and not as restrictive in any form whatsoever. Modifications and variations of the system and apparatus described herein will be obvious to those skilled in the art. Such modifications and variations are intended to come within ambit of the present invention, which is limited only by the appended claims.

It shall be generally noted that at least a major portion of the foregoing disclosures of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in files or records of the receiving Patent Office(s), but otherwise reserves all copyright rights whatsoever. ,CLAIMS:1] A process for treating Spent Pot Lining (SPL) waste to obtain value-added products, the process comprising:
(a) Treating SPL with 15% calcined dolomite fines of size up to 1mm size with retention period of 24 hours to remove moisture and leachable fluorides, whereby calcined dolomite self-hydrates and absorbs moisture from SPL, preventing leachable fluorides from contaminating groundwater.;
(b) Subjecting the treated SPL to heat treatment in ribbon blender at 500oC to break down cyanides, wherein the heat treatment step is performed after mixing SPL with calcined dolomite, ensuring that no fluorides escape into the atmosphere and conducted at a temperature sufficient to decompose cyanides into non-toxic byproducts;
(c) Obtaining a final product which is rich in calcium, magnesium, and other minerals, and free of hazardous cyanides and leachable fluorides, thus making it suitable for use in industrial applications as a fuel or mineralizing agent.

2] The process for treating Spent Pot Lining (SPL) waste to obtain value-added products as claimed in claim 1, wherein the treatment with calcined dolomite results in the following chemical reactions:
(a) 2NaF + CaO.MgO ? CaF2 + MgO + Na2O
(b) 2NaF + CaO.MgO ? CaF2 + MgF2 + Na2O

3] A system for treating SPL waste, comprising:
(d) A reaction chamber for mixing SPL with calcined dolomite and thereby facilitating the controlled hydration of calcined dolomite to absorb moisture and bind fluorides;
(e) A heat treatment unit for breaking down cyanides, said unit being designed to operate at a temperature sufficient to prevent atmospheric escape of hazardous fluorides;
(f) A collection system for the final treated product, which can be used in steel, cement, and ferroalloy industries.