Compositions for the removal of deposits and methods of use

Abstract

The invention provide compositions and method of use for the dissolution of at least one material comprising mercury, lead and / or metal sulphide, the composition comprising an oxidising agent configured to convert at least part of the at least one material to an oxidised solid, and a dissolver agent to dissolve the oxidised solid. The method comprising contacting the composition with the at least one material.

Description

[0001] and Methods of Use

[0002] The present invention relates to compositions and methods for dissolving deposits of hazardous metals. Aspects of the invention relate to methods of removing deposits from pipes, pipelines, pipeline equipment, processing equipment and / or storage vessels involved in oil and gas operations. Aspects of the invention relate to methods of treating radioactive contaminated metals.

[0003] Background to the invention

[0004] During oilfield operations, mercury, lead and metal sulphide salts naturally present in geological formations either in aqueous solution or associated with hydrocarbon liquids and gases may accumulate on the surfaces of pipes and vessels involved in oil production and processing. In particular pipes, vessels, processing equipment and storage vessels on oil producing platforms and floating production storage and offloading (FPSO) units. Downhole production tubing, valves and subsea pipelines transporting hydrocarbon liquids and gases may also become contaminated by mercury, lead and metal sulphides. This contamination may be required to be removed either as part of ongoing remedial treatments to allow for the production operations to be continued or restored. The removal of hazardous contamination may also be required when the platform, FPSO, pipeline or production tubing is being decommissioned.

[0005] Mercury is a toxic metal having harmful effects on the nervous, digestive and immune systems, lungs and kidneys of humans and its effects may be fatal. The inorganic salts of mercury are corrosive to the skin, eyes and gastrointestinal tract, and may induce kidney toxicity if ingested. Mercury therefore can present a significant safety risk to workers that may be exposed to mercury through skin contact or inhalation of mercury vapours. As such, mercury is considered a hazardous substance and its safe removal and disposal is a safety priority.

[0006] Lead is also a toxic metal and the presence of radioactive isotopes of lead such as Pb-210 present further safety hazards to workers that may be exposed to lead and radioactive lead isotopes through skin contact or inhalation. There are oil and gas fields around the world that experience issues with the deposition of sulphide metal scale such as lead sulphide and zinc sulphide. The reason for the formation of damaging metal sulphide scale is that some oilfields have elevated levels of both metals such as lead and hydrogen sulphide gas in their produced waters. Metal sulphide mineral scale deposition on production tubing and topsides oil production vessels can reduce oil flow and the efficiency of oil production operations and the adherence and accumulation of sulphide scale deposits downhole can result in the malfunction of well equipment such as subsurface safety valves which can prevent safety equipment such as valves from operating effectively and compromise well integrity. This may result in unscheduled and prolonged downtime incurring costly remedial treatment and significant lost production.

[0007] There is also an environmental concern that following decommissioning of pipelines especially subsea pipelines, highly toxic metal and metal salts present inside a pipeline can be released into the environment as the metal ions leach into seawater as abandoned pipes on the seabed corrode exposing the toxic metals previously contained within the pipe to the seawater environment. This poses a serious biohazard and threat to the health of living organisms in the surrounding environment.

[0008] During hydrocarbon production and refinement operations low levels of toxic metals such as elemental mercury and lead are present which can precipitate, coalesce and accumulate in vessels, pipes and surfaces. Care must be taken to prevent the toxic metal being released into the surroundings, exacerbating the problem of contamination by spreading the contamination into a larger area and releasing it in a form that may be inhaled.

[0009] At present the available methods for removing liquid mercury, metallic lead and metal sulphides such as lead sulphide are limited and unsatisfactory. Mercury, lead and lead sulphide are insoluble in most solvents and are only sparingly soluble in concentrated acids which creates challenges for their removal. The use of acid treatments to clean up surfaces contaminated with toxic metals is disfavoured because it has limited effectiveness and is a safety hazard to workers. In addition acid treatments may corrode steel surfaces compromising the integrity of equipment, support structures and the well. Summary of the invention

[0010] It is an object of the present invention to obviate or at least mitigate the foregoing disadvantages of toxic metal and mineral deposit removal methods.

[0011] It is another object of an aspect of the present invention to provide a composition which can remove hazardous toxic metal deposits contaminating equipment involved in oil and gas operations including pipelines, piping, downhole equipment, processing equipment and storage vessels in a safe manner which may mitigate environmental threats posed by the contents of decommissioned oil and gas equipment.

[0012] It is another object of an aspect of the present invention to provide a method of removing scale deposits of mercury, lead and metal sulphides such as lead sulphide and zinc sulphide from production tubing and / or valves and equipment associated with production tubing.

[0013] It is a further object of an aspect of the present invention to provide a treatment for pipes and processing equipment and vessels which can work quickly and remotely to remove and / or treat hazardous toxic metal deposits.

[0014] It is a further object of an aspect of the present invention to provide a treatment for pipes and processing equipment and vessels which can work quickly and remotely to remove hazardous radioactive metal deposits.

[0015] Further aims of the invention will become apparent from the following description.

[0016] According to a first aspect of the present invention there is provided a method of dissolving at least one deposit comprising mercury, lead and / or metal sulphide, the method comprising providing a composition comprising an oxidising agent configured to convert at least part of the at least one deposit to an oxidised solid form; and a dissolver agent configured to dissolve the oxidised form.

[0017] The method may comprise contacting the at least one deposit with the composition. The method may comprise dissolving deposits comprising mercury, lead and / or metal sulphide. The oxidising agent may be configured to convert an outer surface of the deposit to an oxidised solid form. The dissolver agent may be configured to dissolve the oxidised outer surface. The oxidising agent may be configured to convert a layer of the deposit to an oxidised layer of the deposit. The dissolver agent may be configured to dissolve the oxidised layer. The non-oxidised form of the deposit may be liquid or solid. The oxidising agent may be selected from the group comprising hydrogen peroxide, inorganic peroxides, halogens, nitric acid, potassium chlorate, sulfuric acid, peroxydisulfuric acid, hypochlorite, chlorite, chlorate and perchlorate. Preferably the oxidising agent comprises hydrogen peroxide. The metal sulphide may be selected from the group comprising lead sulphide and / or zinc sulphide.

[0018] The dissolver agent may comprise carboxylic acid and / or a salt of a carboxylic acid. The carboxylic acid may be selected from the group comprising lactic acid, glycolic acid, gluconic acid, formic acid, citric acid and / or acetic acid. The carboxylate salt may be selected from the group comprising ammonium carboxylate salt, ammonium acetate, ammonium hydroxy acetate and / or ammonium lactate. The dissolver agent may comprise an aminopolycarboxylic acid. The dissolver agent may comprise at least one chelating agent. The at least one chelating agent may be selected from the group comprising ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), diethylenetriaminepentaacetic acid (DTPA), glucoheptonic acid, gluconic acid and their alkali metal and ammonium salts. The composition may comprise from about 5% to about 50% w / w chelating agent. The composition may comprise 10% w / w chelating agent.

[0019] The composition may be an acidic composition. The composition may have a pH in the range of pH 1 to 5. The composition may have a pH equal to or less than pH 2. The composition may be an alkaline composition. The composition may have a pH in the range of pH 8 to 14. The composition may have a pH in the range of pH 10 to 12. The composition may be a neutral composition. The composition may have a pH in the range of 5 to 8. The composition may have a pH of approximately 7. The composition may be a liquid composition. The composition may be a solution. The composition may be an aqueous composition. The composition may comprise from about 5% to about 50% oxidising agent by weight. The composition may comprise from about 10% to about 40% oxidising agent by weight. The composition may comprise from about 15% to about 25% oxidising agent by weight. The composition may comprise from about 30% to about 85% w / w water. The composition may comprise from about 50% to about 80% w / w water. The composition may comprise 38% w / w water. The composition may comprise 55% w / w water. The composition may comprise 76% w / w water. The composition may comprise lactic acid, hydrogen peroxide and water. The composition may comprise 10% to 40% lactic acid, 10% to 40% hydrogen peroxide and 20% to 80% water. The composition may comprise 16% lactic acid, 15% hydrogen peroxide and 76% water. The composition may comprise 32% lactic acid, 30% hydrogen peroxide and 38% water. The composition may comprise 35% ammonium acetate, 15% hydrogen peroxide and 55% water. The composition may comprise 16% acetic acid, 15% hydrogen peroxide and 76% water. The composition may be an acidic pH composition comprising hydrogen peroxide and a carboxylic acid. The composition may be an alkali pH composition comprising hydrogen peroxide and a carboxylate salt. The composition may be an acidic pH composition comprising hydrogen peroxide and either a carboxylic acid or a salt of a carboxylic acid. The composition may be an alkali pH composition comprising hydrogen peroxide and an amino polycarboxylate salt. The composition may be a neutral pH composition comprising hydrogen peroxide and a carboxylate salt. The composition may have a dissolution capacity of up to 1kg solid deposit / litre of composition. The composition may have a dissolution capacity of up to 0.5kg solid deposit / litre of composition. The composition may have a dissolution capacity of about 0.1 kg to about 0.4kg solid deposit / litre of composition. The composition may be configured to be compatible with pipes, pipelines, pipeline joints, seals and gaskets, pipeline equipment, refinery equipment, refinery pipework, vessels and / or processing equipment involved in oil and gas operations such that the composition is not corrosive to pipes, pipelines, pipeline joints, pipeline equipment, vessels and / or processing equipment and does not damage pipes, pipelines and / or pipeline equipment such as joints or seals, vessels and / or processing equipment. The pipes, pipelines, pipeline joints, pipeline equipment, vessels and / or processing equipment may be made of metal. The pipes, pipelines, pipeline joints and / or pipeline equipment, vessels and processing equipment may be made of steel. The pipes, pipelines, pipeline joints, pipeline equipment, vessels and / or processing equipment may be located downhole or topside. The composition may be a one stage treatment. The method may comprise removing insoluble contaminants from surfaces such as pipes and / or vessels. The method may comprise removing insoluble contaminants from surfaces to restore productivity and / or functionality of equipment such as valves. The method may comprise removing insoluble contaminants from surfaces to restore effective processing operations. The method may comprise removing insoluble contaminants from surfaces to remove hazardous contamination. This may allow safe manned entry or may be a necessary procedure as a part of decommissioning work. The method may comprise removing contaminants from surfaces such as pipes and / or vessels. The method may comprise removing contaminants from surfaces to restore productivity and / or functionality of equipment such as valves. The method may comprise removing contaminants from surfaces to restore effective processing operations. The method may comprise removing contaminants from surfaces to remove hazardous contamination. The method may comprise contacting the deposit with the composition for up to 5 minutes. The method may comprise contacting the deposit with the composition for at least 5 minutes. The method may comprise contacting the deposit with the composition for a period of time of at least 30 minutes. The method may comprise contacting the deposit with the composition for a period of time of at least 1 hour. The method may comprise contacting the deposit with the composition for a period of time of between 15 mins and 3 hours. The method may comprise contacting the deposit with the composition for a period of time of between 15 mins to 12 hours. The method may comprise contacting the deposit with the composition for a period of time of between 1 hour and 10 hours to dissolve the deposit. The method may comprise contacting the deposit with the composition for up to 24 hours. The method may comprise contacting the deposit with the composition for at least 24 hours. The period of time of contact may be dependent on the amount of deposit present its size and / or its thickness. The method may comprise maintaining contact for a time sufficient to dissolve the deposit. The method may comprise contacting the deposit with the composition at ambient temperature. Ambient temperature may be the temperature of the air, fluids and / or a surface surrounding or in the location of the deposit or scale. Ambient temperature may be the temperature of the pipes, pipeline, pipeline equipment, processing equipment, and / or storage vessel at the location of the deposit or scale. The method may comprise contacting the deposit with the composition at a temperature in the range of from about 0°C to 90°C. The method may comprise contacting the deposit with the composition at a temperature in the range of from about 20°C to 70°C. The method may comprise contacting the deposit with the composition at a temperature in the range of from about 20°C to 90°C.

[0020] The method of dissolving deposits comprising mercury, lead and / or metal sulphide may be an exothermic reaction. The method may comprise controlling the exothermic reaction by controlling the concentration of the oxidising agent and / or the concentration of the dissolver agent. The method may comprise controlling the ambient conditions of temperature during the dissolution of the deposit by controlling the concentration of the oxidising agent and / or the concentration of the dissolver agent. The higher the concentration of the dissolver solution and / or the oxidiser solution the higher the temperature rise. The method may comprise controlling the rate of reaction of the dissolution of the deposit by controlling the concentration of the oxidising agent and / or the concentration of the dissolver agent. The higher the concentration of the dissolver solution and / or oxidising solution the faster the dissolution rate. The method may comprise mixing the oxidising agent and the dissolver agent before contacting with the at least one deposit. The method may comprise mixing the oxidising agent and the dissolver agent on site and / or immediately before contacting with the at least one deposit.

[0021] According to a second aspect of the present invention there is provided a method of removing scale comprising mercury, lead and / or metal sulphide from a contaminated surface, the method comprising providing a composition comprising an oxidising agent configured to convert at least part of the scale to an oxidised solid form; and a dissolver agent configured to dissolve the oxidised solid; and contacting the scale with the composition.

[0022] The contaminated surface may be a surface of a pipe, pipeline, pipeline equipment, processing equipment, and / or storage vessel previously or currently involved in oil and gas operations. Pipeline equipment may comprise pipeline joints and / or seals. The composition may be configured to be compatible with pipes, pipelines, pipeline joints and / or pipeline equipment such that the composition is not corrosive to pipelines, pipeline joints and / or pipeline equipment and does not damage pipelines and / or pipeline equipment such as joints or seals. The pipelines, pipeline joints and / or pipeline equipment may be made of metal. The pipelines, pipeline joints and / or pipeline equipment may be made of steel. The composition may be configured to be compatible with non-metallic materials used as coatings on pipes, pipelines, pipeline joints and / or pipeline equipment. The coating may comprise a polymer. The coating may comprise an epoxy resin coating. The pipe, pipeline, pipeline equipment, processing equipment, and / or storage vessel may be active or decommissioned. The pipeline may be a hydrocarbon pipeline. The pipeline may be an oil or gas pipeline. The method may comprise removing scale from the pipeline, pipeline equipment, processing equipment and / or storage vessel as part of a maintenance or cleaning operation. The method may comprise removing scale from the pipeline, pipeline equipment, processing equipment and / or storage vessel as part of a decommissioning operation. At least a part of an internal and / or external surface of a pipe, pipeline, pipeline equipment, processing equipment and / or storage vessel may be contaminated with scale comprising mercury, lead and / or metal sulphide. The method may comprise contacting at least a part of an internal and / or external surface of a pipe, pipeline, pipeline equipment, processing equipment and / or storage vessel with the composition. The method may comprise contacting a surface of a pipe, pipeline, pipeline equipment, processing equipment and / or storage vessel contaminated with mercury, lead and / or metal sulphide scale with the composition by passing the composition in, through and / or over the pipeline, pipeline equipment, processing equipment and / or storage vessel . The method may comprise contacting the mercury, lead and / or metal sulphide scale with the composition for less than 5 minutes. The method may comprise contacting the scale with the composition for at least 5 minutes. The method may comprise contacting the scale with the composition for a period of at least 30 minutes. The method may comprise contacting the scale with the composition for a period of at least 1 hour. The method may comprise contacting the scale with the composition for a period of between 1 hour and 10 hours to dissolve the mercury, lead and / or metal sulphide scale. The method may comprise contacting the scale with the composition for up to 24 hours. The method may comprise contacting the scale with the composition for at least 24 hours The period of time of contact may be dependent on the amount of deposit present its size and / or its thickness. The method may comprise contacting the scale with the composition by pumping the composition into and / or through the pipe, pipeline, pipeline equipment, processing equipment and / or storage vessel. The method may involve spraying the composition onto, into and / or through the pipeline, pipeline equipment, processing equipment and / or storage vessel. The method may involve spraying the composition onto the contaminated walls of a vessel. The method may comprise collecting and reapplying composition to a treatment area, The method may comprise spraying the composition onto an upper surface or wall of a vessel. The method may comprise the composition flowing down one or more walls of the vessel. The method may comprise collecting and pumping composition pooling at the bottom of a vessel and reapplying it as a spray to one or more surfaces of the vessel. The method may comprise reapplying composition to a treatment area until the deposit has been dissolved. The method may comprise reapplying composition to a treatment area until the composition has become spent. The method may comprise replacing the spent composition with fresh dissolver agent and / or oxidising agent.

[0023] The method may comprise contacting the mercury, lead and / or metal sulphide scale with the composition at ambient temperature. Ambient temperature may be the temperature of the air, fluids and / or a surface surrounding or in the location of the scale. Ambient temperature may be the temperature of the pipe, pipeline, pipeline equipment, processing equipment, and / or storage vessel at the location of the scale. The method may comprise controlling the temperature during decontamination operations to control the temperature and / or rate of the exothermic dissolution reactions. The method may comprise pumping out the spent composition and dissolved mercury, lead and / or metal sulphide scale from the pipe, pipeline, pipeline equipment, processing equipment and / or storage vessel to dispose of the spent composition and dissolved mercury, lead and / or metal sulphide scale. The method may comprise disposing of spent composition by re-injecting the spent dissolver into a disposal well. The method may comprise returning or locating contaminants in the formation. The method may comprise disposing of spent composition by treating spent composition with a solution of water-soluble salts. The method may comprise precipitating or re-precipitation of contaminant metals as waste that may be disposed of as a solid waste material. The method may comprise mixing the oxidising agent and the dissolver agent before contacting with the scale. The method may comprise mixing the oxidising agent and the dissolver agent on site and / or immediately before contacting with the scale.

[0024] Embodiments of the second aspect of the invention may include one or more features of the first aspect of the invention or its embodiments, or vice versa.

[0025] According to a third aspect of the present invention there is provided a method of removing scale comprising mercury, lead and / or metal sulphide solids from decommissioned oil and gas equipment, the method comprising providing a composition comprising an oxidising agent configured to convert at least part of the scale to an oxidised solid form; and a dissolver agent configured to dissolve the oxidised solid; and contacting the scale with the composition.

[0026] The method may comprise contacting at least a part of an internal and / or external surface of the decommissioned equipment with the composition. The method may comprise dissolving mercury, lead and / or metal sulphide scale with the composition. The method may comprise contacting the mercury, lead and / or metal sulphide scale with the composition by pumping the composition in, over and / or through the decommissioned equipment. The method may comprise contacting the mercury, lead and / or metal sulphide scale with the composition at ambient temperature. The method may comprise contacting the mercury, lead and / or metal sulphide scale with the composition at 20°C. The method may comprise contacting the mercury, lead and / or metal sulphide scale with the composition at between 10°C and 50°C. The method may comprise contacting the mercury, lead and / or metal sulphide scale with the composition at between 20°C and 90°C. The method may comprise pumping out spent composition and / or dissolved mercury, lead and / or metal sulphide scale from the decommissioned equipment. The decommissioned equipment may have previously been used in oil and gas operations. The decommissioned equipment may be selected from pipes, pipeline, pipeline equipment, storage vessels and / or processing equipment. The pipeline may comprise surface and / or subsea pipeline.

[0027] Embodiments of the third aspect of the invention may include one or more features of the first or second aspects of the invention or their embodiments, or vice versa.

[0028] According to a fourth aspect of the present invention there is provided a method of treating a contaminated surface to remove scale comprising mercury, lead and / or metal sulphide solids, the method comprising contacting scale with a composition comprising an oxidising agent configured to convert at least part of the scale to an oxidised solid; and a dissolver agent to dissolve the oxidised solid.

[0029] The method may comprise contacting mercury, lead and / or metal sulphide scale on at least a part of a surface with the composition. The contaminated surface may be a surface of a pipe, pipeline, pipeline equipment, processing equipment, and / or storage vessel previously or currently involved in oil and gas operations. The method may comprise contacting at least a part of an internal and / or external surface of a pipeline with the composition. The method may comprise contacting at least a part of an internal and / or external surface of a piece of pipeline equipment with the composition.

[0030] Embodiments of the fourth aspect of the invention may include one or more features of any of the first to third aspects of the invention or their embodiments, or vice versa.

[0031] According to a fifth aspect of the present invention there is provided a composition for the dissolution of at least one deposit comprising mercury, lead and / or metal sulphide, the composition comprising an oxidising agent configured to convert at least part of the at least one deposit to an oxidised solid; and a dissolver agent to dissolve the oxidised solids.

[0032] The composition may be for use in the dissolution of deposits comprising mercury, lead and / or metal sulphide. The oxidising agent may be selected from the group comprising hydrogen peroxide, inorganic peroxides, halogens, nitric acid, potassium chlorate, sulfuric acid, peroxydisulfuric acid, hypochlorite, chlorite, chlorate and perchlorate. Preferably the oxidising agent comprises hydrogen peroxide. The metal sulphide may be lead sulphide or zinc sulphide. The dissolver agent may comprise carboxylic acid and / or a salt of a carboxylic acid. The carboxylic acid may be selected from the group comprising lactic acid, glycolic acid, gluconic acid, formic acid, citric acid and / or acetic acid. The carboxylate salt may be selected from the group comprising ammonium carboxylate salt, ammonium acetate, ammonium hydroxyacetate and / or ammonium lactate. The dissolver agent may comprise an aminopolycarboxylic acid. The dissolver agent may comprise at least one chelating agent. The at least one chelating agent may be selected from the group comprising ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), diethylenetriaminepentaacetic acid (DTPA),glucoheptonic acid and gluconic acid and their alkali metal and ammonium salts. The composition may comprise from about 5% to about 50% w / w chelating agent. The composition may comprise 10% w / w chelating agent.

[0033] The composition may be an acidic composition. The composition may have a pH in the range of pH 1 to 5. The composition may have a pH equal to or less than pH 2. The composition may be an alkaline composition. The composition may have a pH in the range of pH 8 to 14. The composition may have a pH in the range of pH 10 to 12. The composition may be a neutral composition. The composition may have a pH in the range of 5 to 8. The composition may have a pH of approximately 7. The composition may be a liquid composition. The composition may be a solution. The composition may be an aqueous composition.

[0034] The composition may comprise from about 5% to about 50% oxidising agent by weight. The composition may comprise from about 10% to about 40% oxidising agent by weight. The composition may comprise from about 15% to about 25% oxidising agent by weight. The composition may comprise from about 5% to about 50% dissolver agent by weight. The composition may comprise from about 10% to about 40% dissolver agent by weight. The composition may comprise from about 15% to about 25% dissolver agent by weight. The composition may comprise from about 30% to about 85% w / w water. The composition may comprise from about 50% to about 80% w / w water. The composition may comprise 38% w / w water. The composition may comprise 55% w / w water. The composition may comprise 76% w / w water. The composition may comprise lactic acid, hydrogen peroxide and water. The composition may comprise 10% to 40% lactic acid, 10% to 40% hydrogen peroxide and 20% to 80% water. The composition may comprise 16% lactic acid, 15% hydrogen peroxide and 76% water. The composition may comprise 32% lactic acid, 30% hydrogen peroxide and 38% water. The composition may comprise 35% ammonium acetate, 15% hydrogen peroxide and 55% water. The composition may comprise 16% acetic acid, 15% hydrogen peroxide and 76% water. The composition may be an acidic pH composition comprising hydrogen peroxide and at least one carboxylic acid. The composition may be an alkali pH composition comprising hydrogen peroxide and at least one carboxylate salt. The composition may be a neutral pH composition comprising hydrogen peroxide and at least one carboxylate salt. The composition may have a dissolution capacity of up to 1 kg solid deposit / litre of composition. The composition may have a dissolution capacity of up to 0.5kg solid deposit / litre of composition. The composition may have a dissolution capacity of about 0.1kg to about 0.4kg solid deposit / litre of composition.

[0035] The composition may be configured to be compatible with metal pipes, pipelines, pipeline joints, pipeline equipment, processing equipment, and / or storage vessels such that the composition is not corrosive to pipes, pipelines, pipeline joints, pipeline equipment, processing equipment, and / or storage vessels and does not damage pipes, pipelines and / or pipeline equipment such as joints or seals. The composition may be a treatment fluid. The mercury, lead and / or metal sulphide deposits may be in the form of a scale. The composition may be provided as a treatment for pipes, pipelines, decommissioned pipelines, surface pipelines, subsea pipelines, pipeline equipment, processing equipment, and / or storage vessels to dissolve and / or remove scale deposits comprising mercury, lead and / or metal sulphide. The scale deposits comprising mercury, lead and / or metal sulphide solids may be present on at least an internal and / or external surface of at least part of the pipe, pipelines, decommissioned pipelines, surface pipelines, subsea pipelines, pipeline equipment, processing equipment, and / or storage vessels.

[0036] Embodiments of the fifth aspect of the invention may include one or more features of any of the first to fourth aspects of the invention or their embodiments, or vice versa.

[0037] According to a sixth aspect of the present invention there is provided a composition for use in the removal of scale comprising mercury, lead and / or metal sulphide, the composition comprising an oxidising agent configured to convert at least part of the scale to an oxidised solid; and a dissolver agent to dissolve the oxidised solid.

[0038] The contaminated surface may be a surface of a pipe, pipeline, pipeline equipment, processing equipment, and / or storage vessel previously or currently involved in oil and gas operations. The surface may be at least a part of an internal and / or external surface of a pipeline, pipeline equipment, processing equipment, and / or storage vessel. The pipe, pipeline, pipeline equipment, processing equipment, and / or storage vessel may be an active pipe, pipeline, pipeline equipment, processing equipment, and / or storage vessel. The pipe, pipeline, pipeline equipment, processing equipment, and / or storage vessel may be decontaminated by removing scale as part of a maintenance or cleaning operation. The pipe, pipeline, pipeline equipment, processing equipment, and / or storage vessel may be decommissioned. The pipe, pipeline, pipeline equipment, processing equipment, and / or storage vessel may be decontaminated by removing scale as part of a decommissioning operation. The composition may be configured to be compatible with metal pipes, pipelines, pipeline joints pipeline equipment, processing equipment, and / or storage vessels such that the composition is not corrosive to pipes, pipelines, pipeline joints, pipeline equipment processing equipment, and / or storage vessels and does not damage joints or seals. The composition may be a treatment fluid. The composition may be provided as a treatment for pipelines, decommissioned pipes, pipelines, surface pipelines, subsea pipelines , pipeline equipment, processing equipment, and / or storage vessels to dissolve and / or remove scale deposits comprising mercury, lead and / or metal sulphide. The scale deposits comprising mercury, lead and / or metal sulphide solids may be present on at least an internal and / or external surface of the pipes, pipeline, pipeline equipment, processing equipment, and / or storage vessels.

[0039] Embodiments of the sixth aspect of the invention may include one or more features of any of the first to fifth aspects of the invention or their embodiments, or vice versa.

[0040] According to a seventh aspect of the present invention there is provided a method of separating materials comprising mercury, lead and / or metal sulphide contaminated with radioactive material from the radioactive material; the method comprising contacting mercury, lead and / or metal sulphide material with a composition comprising an oxidising agent configured to convert at least part of the mercury, lead and / or metal sulphide materials to an oxidised solid form; and a dissolver agent configured to dissolve the oxidised solid; and separating the radioactive material from the mercury, lead and / or metal sulphide material.

[0041] The method may comprise dissolving the mercury, lead and / or metal sulphide material. The method may comprise separating the soluble non-radioactive material (mercury, lead and / or metal sulphide material) from the insoluble radioactive material. The method may comprise decontaminating lead shielding such as bricks used in nuclear reactors are contaminated with non-lead radioisotopes that have become activated through the process of neutron bombardment.

[0042] Embodiments of the seventh aspect of the invention may include one or more features of any of the first to sixth aspects of the invention or their embodiments, or vice versa. According to an eighth aspect of the present invention there is provided a method of decontaminating lead shielding material used in nuclear reactors contaminated with radioactive material; contacting contaminated lead shielding material with a composition comprising an oxidising agent configured to convert at least part of the lead shielding material to an oxidised solid form; and a dissolver agent configured to dissolve the oxidised solid; and separating the radioactive material from the dissolved lead material.

[0043] The lead shielding may be lead shielding bricks. The radioactive material may be radioisotopes. The radioactive material may be non-lead radioisotopes.

[0044] The composition may be used to dissolve radioactive lead for disposal. The method may comprise dissolving non-radioactive lead leaving behind insoluble radioactive metal contaminants for disposal. The oxidising agent may be selected from the group comprising hydrogen peroxide, inorganic peroxides, halogens, nitric acid, potassium chlorate, sulfuric acid, peroxydisulfuric acid, hypochlorite, chlorite, chlorate and perchlorate. Preferably the oxidising agent comprises hydrogen peroxide. The dissolver agent may comprise carboxylic acid and / or a salt of a carboxylic acid. The carboxylic acid may be selected from the group comprising lactic acid, glycolic acid, gluconic acid, formic acid, citric acid and acetic acid. The carboxylate salt may be selected from the group comprising ammonium carboxylate salt, ammonium acetate, ammonium hydroxyacetate and / or ammonium lactate. The dissolver agent may comprise an aminopolycarboxylic acid. The dissolver agent may comprise at least one chelating agent. The at least one chelating agent may be selected from the group comprising ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), diethylenetriaminepentaacetic acid (DTPA), glucoheptonic acid, gluconic acid and their alkali metal and ammonium salts. The composition may comprise from about 5% to about 50% w / w chelating agent. The composition may comprise 10% w / w chelating agent.

[0045] Embodiments of the eighth aspect of the invention may include one or more features of any of the first to seventh aspects of the invention or their embodiments, or vice versa.

[0046] According to a ninth aspect of the present invention there is provided a composition for the dissolution of at least one material comprising mercury, lead and / or metal sulphide, the composition comprising an oxidising agent configured to convert at least part of the at least one material to an oxidised form; and a dissolver agent to dissolve the oxidised form.

[0047] The oxidised form may be an oxidised solid. The oxidising agent may be selected from the group comprising hydrogen peroxide, inorganic peroxides, halogens, nitric acid, potassium chlorate, sulfuric acid, peroxydisulfuric acid, hypochlorite, chlorite, chlorate and perchlorate. The metal sulphide may be lead sulphide or zinc sulphide. The dissolver agent may comprise carboxylic acid and / or a salt of a carboxylic acid.

[0048] The dissolver agent may comprise at least one chelating agent selected from the group comprising ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), diethylenetriaminepentaacetic acid (DTPA),glucoheptonic acid and gluconic acid and their alkali metal and ammonium salts. The composition may comprise about 10% to about 40% oxidising agent by weight. The composition may comprise about 5% to about 50% dissolver agent by weight. The composition may comprise about 30% to about 85% w / w water. The composition may comprise an acidic pH composition comprising hydrogen peroxide and at least one carboxylic acid. The composition may comprise an alkali pH composition comprising hydrogen peroxide and at least one carboxylate salt. The composition may comprise a neutral pH composition comprising hydrogen peroxide and at least one carboxylate salt. The composition may comprise lactic acid, hydrogen peroxide and water. The composition may comprise ammonium acetate, hydrogen peroxide and water. The composition may comprise acetic acid, hydrogen peroxide and water.

[0049] Embodiments of the ninth aspect of the invention may include one or more features of any of the first to eighth aspects of the invention or their embodiments, or vice versa.

[0050] According to a tenth aspect of the present invention there is provided a method of dissolving at least one material comprising mercury, lead and / or metal sulphide, the method comprising providing a composition comprising an oxidising agent configured to convert at least part of the material to an oxidised form; and a dissolver agent configured to dissolve the oxidised form; contacting the at least one material with the composition. The oxidised form may be an oxidised solid. The oxidising agent may be configured to convert an outer surface of the material to an oxidised form and wherein the dissolver agent is configured to dissolve the outer surface. The oxidising agent may be selected from the group comprising hydrogen peroxide, inorganic peroxides, halogens, nitric acid, potassium chlorate, sulfuric acid, peroxydisulfuric acid, hypochlorite, chlorite, chlorate and perchlorate.

[0051] The dissolver agent may comprise carboxylic acid and / or a salt of a carboxylic acid. The composition may comprise hydrogen peroxide and water and at least one of lactic acid, ammonium acetate or acetic acid. The method may comprise contacting the material with the composition for a period of between 15 mins and 12 hours. The method may comprise contacting the material with the composition at a temperature in the range of from about 20°C to 90°C. The method may comprise contacting the material with the composition for a period of between 15 mins and 3 hours. The method may comprise contacting the material with the composition at a temperature in the range of from about 20°C to 70°C. The at least one material may be a deposit or scale. The method may comprise contacting or spraying the composition on, in or through pipes, pipelines, pipeline joints, seals and gaskets, pipeline equipment, refinery equipment, refinery pipework, vessels and / or processing equipment involved in oil and gas operations, nuclear reactors and / or lead shielding materials. The method may comprise replacing spent composition with fresh dissolver agent and / or oxidising agent.

[0052] The at least one material may be contaminated with radioactive material. The method may comprise separating the at least one material contaminated with radioactive material from the radioactive material. The method may comprise separating the at least one material comprising mercury, lead and / or metal sulphide contaminated with radioactive material from the radioactive material by dissolving the mercury, lead and / or metal sulphide materials and separating the insoluble radioactive material from the soluble material.

[0053] Embodiments of the tenth aspect of the invention may include one or more features of any of the first to ninth aspects of the invention or their embodiments, or vice versa. According to an eleventh aspect of the present invention there is provided a use of a composition according to any of the fifth, sixth or ninth aspects of the invention for the dissolution of at least one material comprising mercury, lead and / or metal sulphide.

[0054] The at least one material may be a deposit or scale. The at least one material may be a lead shielding material. The lead shielding material may be contaminated with radioactive material.

[0055] Embodiments of the eleventh aspect of the invention may include one or more features of any of the first to tenth aspects of the invention or their embodiments, or vice versa.

[0056] According to a twelfth aspect of the present invention there is provided a use of a composition according to any of the fifth, sixth or ninth aspects of the invention for decontaminating lead shielding material used in nuclear reactors contaminated with radioactive material.

[0057] Embodiments of the twelfth aspect of the invention may include one or more features of any of the first to eleventh aspects of the invention or their embodiments, or vice versa.

[0058] According to a thirteenth aspect of the present invention there is provided a method of using a composition according to any of the fifth, sixth or ninth aspects of the invention for dissolving at least one material comprising mercury, lead and / or metal sulphide.

[0059] Embodiments of the thirteenth aspect of the invention may include one or more features of any of the first to twelfth aspects of the invention or their embodiments, or vice versa.

[0060] Brief description of the drawings

[0061] There will now be described, by way of example only, an embodiment of the invention with reference to the drawing, of which:

[0062] Figure 1 is a diagram illustrating the oxidisation of mercury by hydrogen peroxide and the dissolution of mercury oxide by lactic acid to form mercury lactate using a composition according to an embodiment of the invention; Figure 2 is a graph showing a dissolution curve of mercury in contact with a composition according to an embodiment of the invention;

[0063] Figure 3 is a graph showing the formation sulphur, thiosulphate and sulphate during the oxidation of lead sulphate under acidic conditions (pH 2);

[0064] Figures 4A and 4B are images showing lead sulphide in a composition according to an embodiment of the invention at T= Omins and T=12hrs respectively;

[0065] Figures 5A and 5B are images showing lead sulphide solid in contact with a composition according to an embodiment of the invention at T= Omins and T=12hrs respectively;

[0066] Figure 6 is a graph showing the formation sulphur, thiosulphate and sulphate during the oxidation of lead sulphate under neutral conditions (pH 7);

[0067] Figures 7A to 7E are images showing lead sulphide solid in contact with a composition according to an embodiment of the invention at T= Omins, T= 5mins T= 10mins T= 15mins and T=30mins respectively;

[0068] Figure 8 is a graph showing dissolution curves of Galena in contact with a composition according to an embodiment of the invention;

[0069] Figure 9 is a graph showing a temperature curve and dissolution curve of Gelena in contact with a composition according to an embodiment of the invention;

[0070] Figure 10 is a graph showing the formation sulphur, thiosulphate and sulphate during the oxidation of lead sulphate under alkaline conditions (pH 10);

[0071] Figure 11 is a graph showing a dissolution curve of Galena in contact with a composition according to an embodiment of the invention;

[0072] Figure 12 is an illustration of the degradation of EDTA by hydrogen peroxide; and Figures 13A and 13B are images showing zinc sulphide in a composition according to an embodiment of the invention at T= Omins and T=3hrs respectively.

[0073] Description of the preferred embodiments

[0074] The invention will be further illustrated by the following examples. The invention will be illustrated by means of tests made by the inventor which demonstrate the effectiveness of the process of removing toxic metal and mineral deposits. This example is included to demonstrate the use of the compositions in accordance with embodiments of the present invention. Various modifications to the described example may be made within the scope of the invention.

[0075] Example 1

[0076] The insoluble deposit in this example is elemental mercury which is a toxic heavy metal which can contaminate surfaces as liquid spheres or globules. A first stage involves oxidizing the deposit by contacting the deposit with an oxidizing agent in the formulation. In this example the oxidising agent is Hydrogen Peroxide (H2O2). The concentration of oxidizing agent required for optimal performance varies with the deposit being oxidized.

[0077] The oxidization of mercury, can be described by the following reactions:

[0078] Hg°(l)+ H2O2 -» HgO(s) + H2O (1 )

[0079] A second stage of the process involves dissolving the oxidized deposit. In this example the dissolver agent is a carboxylic acid, lactic acid. Lactic acid when combined with hydrogen peroxide produces a dissolver that produces a clear solution as it dissolves mercury to form mercury lactate.

[0080] HgO(s)+ 2CH3CH(OH)CO2H (aq) Hg(CH3CH(OH)CO2)2(aq) + H2O (2)

[0081] The oxidation takes place in aqueous solution where the outer surfaces of the deposits are in contact with the oxidizing agent. The oxidized outer surfaces can then react with the dissolver agent present in the formulation to solubilize them and expose fresh deposit surface to the oxidizing agent for it, in turn, to become solubilized as divalent metal ions in aqueous solution. During the reaction bubbles of oxygen are seen streaming from the surface of the mercury globule. Mercuric oxide is formed as the mercury is oxidized at the surface by the hydrogen peroxide and is soluble in lactic acid. Mercuric oxide can be further oxidized by reaction with a further hydrogen peroxide molecule to form mercury ions in aqueous solution and oxygen. The divalent mercury ions can then be sequestered by the lactic acid to form mercury lactate. The oxidising agent and dissolver agent have a cyclic relationship where the oxidising agent oxidises outer exposed surfaces and the dissolver agent dissolves the oxidised surfaces exposing new surfaces for the oxidising agent.

[0082] HgO(s) + H2O2(aq) - Hg2+(aq)+ O2(g) + H2O (3)

[0083] Mercuric Lactate

[0084] Figure 1 is an illustration of the oxidation of mercury by hydrogen peroxide and the dissolution of mercury oxide by lactic acid to form mercuric lactate. In this example a composition of 30 grams of Hydrogen Peroxide (50%w / w) is added to 20 grams of Lactic Acid (80%w / w) to make 50 grams of a 30:32:38 H2O2: Lactic Acid: Water mix (specific gravity =1 ,165g / cm3). A small droplet of mercury weighing 0.34g was added to 25cm3of the 30:32:38 formulation. The droplet was removed and weighed during a four hour period of incubation at 20°C. Figure 2 shows the dissolution curve for the droplet. The shiny mercury sphere remained shiny during the dissolution and produced a fine stream of small bubbles as mercury and mercuric oxide was oxidized by the hydrogen peroxide. The solution remained clear and colourless as the mercury completely dissolved at approximate 4.2 hours. In order to determine capacity, 5 ml of the 30:32:38 Hydrogen Peroxide: Lactic acid: Water composition dissolved 1.27 grams of elemental mercury representing a dissolution capacity of 254g Hg / litre. Example 2

[0085] In this example the insoluble deposit is Lead that may contaminate surfaces as a solid metallic lead coating which is toxic. A more problematical form of lead may present as a Naturally Occurring Radioactive Material (NORM) hazard through the presence of the radioisotope Pb-210. Whereas lead metal and lead mineral ores formed over thousands to millions of years ago are stable and are devoid of the isotope Pb-210 because any radioactive lead has long since decayed (half-life for Pb-210 is 22.3 years), freshly deposited lead in oilfield applications, where the lead originates from formation waters containing the decaying daughters of Uranium for instance may contain Pb-210 so that any freshly deposited lead or lead salt contains radioactive Pb-210 alongside stable Pb- 206 and considered as a Naturally Occurring Radioactive Material (NORM). In instances where lead scale deposits occur in oilfield operations the lead itself is regarded as a hazardous radioactive deposit that needs to be removed due to safety implications of people being exposed to a hazardous environment.

[0086] The same hydrogen peroxide: lactic acid formulation used in Example 1 to dissolve elemental mercury was used to dissolve metallic lead. The concentration of hydrogen peroxide (30%w / w) and lactic acid (32%w / w) was found to be higher than necessary for the dissolution of lead and causes a vigorous exothermic reaction with lead. A 50% dilution of the formulation is sufficient for the rapid dissolution of lead and allows a more controlled reaction.

[0087] A first deposit of Lead weighing 6.56g was immersed in 30.0g of a solution of 60% w / w H2O2 (50%):40% Lactic Acid (80%). Specific Gravity of the dissolver was 1.165g / cm3. The lead bubbled vigorously within the first 0.2hrs. Reaction is exothermic so a Duran bottle was immersed in a bath of ice water to control the dissolution rate. The lead deposit was completely dissolved in 30 minutes. A second lead deposit weighing 1.93g was added to the formulation which also dissolved completely. A third lead deposit weighing 4.10g was added to the formulation of which 1.03g dissolved leaving 3.08g of undissolved lead. The total lead dissolved in 30.0g of the composition was 9.52g. The 30.00g Dissolver occupied a volume of 25.75mls giving a Lead dissolution capacity of 369.7g / L The reactions of Example 2 can be described by the following:

[0088] Pb(s) + H2O2 PbO(s) + H2O (4) PbO(s)+ 2CH3CH(OH)CO2H (aq) - Pb(CH3CH(OH)CO2)2(aq) + H2O(I) (5)

[0089] Advantages of using lactic acid are that it is odourless and also can be supplied as a solid powder for some applications minimising transportation and storage of water. However, it will be appreciated that additional or alternative dissolver agents comprising carboxylic acid or salts of carboxylic acids may be used.

[0090] Following decontamination of surfaces contaminated by mercury or lead, the composition containing water-soluble salts of mercury and lead in particular carboxylate salts of mercury and lead, such as mercury lactate, lead lactate and lead acetate may require to be isolated as solids for disposal. This may be achieved by adding a water-soluble salt that reacts with the water-soluble mercury or lead salt to form an insoluble solid precipitate of mercury or lead. A solution of sodium sulphide is one such solution that can be added to spent dissolver containing dissolved mercury or lead carboxylate to precipitate mercury sulphide or lead sulphide for isolation by filtration and disposal as a minimal mass of insoluble metal sulphide.

[0091] One possible application of the dissolver formulation is the decontamination and recycling of lead bricks used as radioactivity shielding in the nuclear industry. During operation, the lead bricks may become radioactive due to bombardment by neutrons which activate metallic elements in the lead bricks thereby forming radioactive isotopes. Lead itself is not activated by neutron bombardment but activation of the shielding bricks may occur as a result of the addition of antimony during the manufacture of the lead bricks to improve the physical characteristics of the bricks. Antimony is often added to the lead shielding bricks at a concentration of around 6%w / w. Antimony is prone to activation the main isotopes being Sb-120, Sb-122 and Sb-124 and the presence of other metals in the lead brick such as Bismuth, which also are susceptible to activation, results in the occurrence of other metallic radioactive isotopes such as Bi-207. The formulations of the present invention may be used to dissolve lead and not dissolve either Bismuth or Antimony. The stable lead may therefore be separated from the radioactive antimony and bismuth activated radioisotopes because the antimony and bismuth remain as solid sludge whilst the lead is in aqueous solution as lead lactate which can be filtered and treated to recover the lead either by electro-deposition or precipitation as a lead salt. The following Examples 3 to 5 illustrate the process of developing a formulation to dissolve lead sulphide and how pH conditions affect the oxidation of the sulphide and the speciation of the sulphoxy products formed during oxidation and how the pH conditions affect the dissolution of the oxidised solids. The terms acidic, neutral, and alkaline conditions relate to the pH of the composition.

[0092] Example 3 Lead Sulphide under acidic conditions

[0093] The solid deposit in this example is a salt of a metal rather than the elemental metal itself. The insoluble deposit in this example is mineral scale deposit lead sulphide which may present a NORM hazard but more usually presents a problem where deposition as a mineral scale deposit adversely affects the operation of equipment such as safety valves.

[0094] Elevated levels of lead and zinc in formation water occur due to leaching of mineral ore deposits that are naturally present in reservoir geological formations where lead sulphide ore such as Galena and zinc sulphide ore or Sphalerite are present. In some oilfield formations the high temperature and high pressure conditions existing in the reservoir have resulted in the dissolution or leaching of these mineral ores over millions of years by water present in the pores of the rock resulting in formation waters that have high levels of lead and zinc divalent cations Pb2+and Zn2+in aqueous solution. Hydrogen sulphide gas can form in reservoirs naturally through geochemical processes where organic matter, laid down to become sedimentary rock, has decomposed to form hydrogen sulphide gas. It can also form as a by-product of the metabolism of sulphate reducing bacteria which can be unintentionally introduced into the formation as a result of seawater injection to maintain reservoir pressure, as oil becomes depleted, during secondary oil recovery methods.

[0095] The diffusion of hydrogen sulphide gas into the formation water results in its dissociation to form sulphide and bisulphide anions S2' and HS'. The mixing of formation water, rich in lead and zinc ions, with waters containing dissociated hydrogen sulphide anions in produced water, results in the precipitation of lead sulphide and zinc sulphide solid deposits. In a first step of this example the lead sulphide is converted to a more soluble metal sulphate form in aqueous solution. In this example the conversion is achieved by the oxidation of sulphide to sulphate using an oxidising agent such as hydrogen peroxide.

[0096] PbS(s) + 4H2O2-» PbSO4(s) + 4H2O (7)

[0097] During the reaction various sulphur containing ions are formed as a result of oxidising sulphide such as sulphur, thiosulphate and tetrathionate as well as sulphate which vary as a function of time of oxidation and the pH conditions.

[0098] Under all conditions of pH the immediate oxidation reaction appears to be one where lead sulphide is oxidised to produce lead hydroxide and elemental sulphur

[0099] 2PbS(s) + 2H2O + O22Pb(OH)2+2S (8)

[0100] Under neutral and alkaline conditions discussed further in examples 4 and 5 , a further reaction occurs rapidly resulting in the formation of lead thiosulphate.

[0101] Finally, the decomposition of thiosulphate occurs as a slower oxidation step resulting in the formation of lead sulphate

[0102] The fact that the lead sulphide has the potential to be transformed into sulphur, thiosulphate and sulphate by immersing the lead sulphide in a solution of converting agent comprising a suitable oxidising agent provides an opportunity to increase the solubility of the lead sulphide.

[0103] In this example the composition is an acidic solution at an approximate pH of 2, lead sulphide oxidises almost exclusively to form sulphur and lead ions (Equation 8). Figure 3 shows concentration of sulphur, thiosulphate and sulphate during the oxidation of lead sulphide under acidic conditions. Under acidic conditions the oxidation of lead sulphide by hydrogen peroxide results primarily in the formation of lead hydroxide and sulphur (solid line) (Equation 8). After a while, sulphate ions (dotted line) are detected but the oxidation of sulphur to sulphate is slow compared with the initial rate of oxidation of lead sulphide. In more acidic solutions where the pH is less than 1.5 the sulphur provides a thermostatically stable oxidation product so that sulphate is virtually absent. The hydrogen peroxide can be blended with a carboxylic acid to create acidic conditions. The lead hydroxide formed through oxidation of the lead sulphide may be soluble in a carboxylic acid such as acetic acid, resulting in lead acetate and water as shown in Equation 11.

[0104] The by-product of the oxidation reaction (as shown in Equation 8) is elemental solid sulphur. Particulate lead sulphide has a large surface area allowing the oxidation and dissolution of lead sulphide to proceed to completion resulting in a clear solution of lead acetate and a suspension of yellow sulphur particles.

[0105] Figure 4A is an image showing analytical grade lead sulphide added to oxidising solution of sodium acetate buffered at pH 4 with acetic acid at 20°C. Figure 4B shows the solution after 12 hours where the lead sulphide is dissolved to form lead acetate and sulphur.

[0106] Figure 5A is an image when lead sulphide is present as a large lump, in this case as crystalline Galena exposed to the oxidising solution of sodium acetate buffered at pH 4 with acetic acid at 20°C. Figure 5B shows limited dissolution after 12 hours where the formation of sulphur as a coating after a short time prevents the dissolution of the lead hydroxide-converted surface layer.

[0107] Example 4 Lead Sulphide under neutral conditions

[0108] During the oxidation of lead sulphide under neutral conditions, lead sulphide is oxidised to form thiosulphate, sulphate and lead ions, along with a small amount of sulphur as expressed in Equations 8 to 10 above. Figure 6 shows the concentration of sulphur, thiosulphate and sulphate during the oxidation of lead sulphide under neutral conditions. The nature of the principal oxidation products depends on the time of oxidation where the main initial oxidation reaction is the formation of thiosulphate (dashed line) which decomposes after time to form sulphate ions (dotted line) which under neutral conditions is the predominant form of sulphur in solution at equilibrium. The quantity of sulphur (solid line) is approximately constant throughout the oxidation. The amount of thiosulphate was found to increase initially and then to remain constant for the rest of the oxidation. No sulphate was detected initially but, the quantity of sulphate was found to increase with time, overtaking the quantity of thiosulphate in solution. The time of these various reactions will depend on the concentration of oxidising agent, and other parameters such as surface area: volume ratio and temperature.

[0109] At pH 7 the oxidation of lead sulphide results principally in the formation of lead sulphate. Whilst the lead sulphate formed is less water soluble than the lead thiosulphate and lead hydroxide it offers the advantage that no significant amount of sulphur is produced under neutral conditions and most significantly, lead sulphate is soluble in ammonium salts. A solution of ammonium carboxylate can be used to dissolve the lead sulphate formed through oxidation of the lead sulphide under neutral pH conditions.

[0110] In this example, a 1.52g cubic crystal of Galena (lead sulphide) was immersed in 50 ml of formulation comprising 35%w / w solution of Ammonium Acetate in combination with 10%w / w hydrogen peroxide. The solid Galena dissolved almost completely in around 1 hour. Figure 7A to 7E show the gradual dissolution of Galena at 0 min, 5min, 10 min, 15 min and 30 min intervals respectively. The reaction between the formulation and Galena is exothermic and depending on the concentration of oxidising agent and ammonium salt, together with the lead sulphide surface area: dissolver volume ratio, can lead to significantly elevated temperatures which accelerates the dissolution rate of lead sulphide deposits. The optimum concentration of components in the formulation can be adjusted by dilution depending on the mineralogy of the metal sulphide deposits formed in the field.

[0111] Figure 8 shows a graph of the dissolution of Galena crystal at 20°C in formulations comprising 35%w / w solution of Ammonium Acetate in combination with either 5%w / w Hydrogen Peroxide (crosses) or 10%w / w hydrogen peroxide (circles). The 1.52g solid Galena in the 10%w / w Hydrogen Peroxide formulation was almost completely dissolved in around 60mins. The 1 ,52g solid Galena in the 5%w / w Hydrogen Peroxide formulation was reduced to 50% at around 80mins, the solid Galena was reduced to 0.3g at 400mins. Figure 9 shows a temperature curve (dashed line) during the dissolution of 0.58g Galena crystal in 30 ml of formulation 1 (15% oxidising agent (Hydrogen Peroxide) and 35% w / w ammonium salt). Figure 9 shows a temperature increase from 20°C to 50°C during the dissolution of a 0.58g Galena crystal in the first 20 minutes of dissolution.

[0112] Example 5 Lead Sulphide under basic conditions

[0113] Figure 10 shows the concentration of sulphur, thiosulphate and sulphate during the oxidation of lead sulphide under basic conditions. Under alkaline conditions at pH 10, lead sulphide is oxidised to produce thiosulphate (dashed line) as the major oxidation product. Small amounts of sulphur (solid line) and tetrathionate ions may also be present but insufficient to significantly inhibit the dissolution of the lead sulphide in the way that sulphur does under acidic conditions. Under alkaline conditions the thiosulphate is more stable with respect to disproportionation than in neutral pH solutions resulting in a greater concentration of lead ions in aqueous solution for a longer period and therefore provides optimum pH conditions for the sequestration of these metal ions by a chelating agent. The formation of tetrathionate results from oxidation of thiosulphate but this is a relatively slow process compared with the process of sequestration.

[0114] The rate of oxidation was found to be linear in all the various pH solutions until the formation of sulphate ions when a significant decrease in reaction rate occurs. The slowest overall reaction rate is in neutral solutions where sulphate is found to be the predominant oxidation species. The fastest overall rate is in acid solutions where the formation of sulphate is least.

[0115] When the lead sulphide is oxidized by hydrogen peroxide under alkaline conditions, the primary form of oxidized lead sulphide is lead thiosulphate. Lead thiosulphate is the most soluble of the lead sulphoxy salts formed by oxidation and might be considered as the easiest to dissolve. Under alkaline conditions a chelating agent such as EDTA as its tetra sodium salt can be blended with hydrogen peroxide to sequester the lead ions in aqueous solution resulting from the solubility of the lead thiosulphate formed as a result of oxidation in hydrogen peroxide. A fresh blend of EDTANa4 and H2O2 dissolves particulate lead sulphide very quickly and a solution containing EDTANa4 : H2O2 (20%w / w :20%w / w) dissolved lead sulphide (8g / 100mls) in five minutes at 20°C and resulted in a clear colourless solution. The chelating agent may be degraded by the hydrogen peroxide and may cease to work after several hours. The dissolution of lumps of lead sulphide requires much more time and the performance of the dissolver diminishes with time because of the incompatibility of the EDTA with the peroxide. When a lump of Galena weighing 2g was immersed in a solution of EDTANa4 and H2O2 (20%w / w:20%w / w) the initial rapid dissolution rate quickly diminished so that no further weight loss of lead sulphide was seen after 60 minutes.

[0116] Figure 11 is a graph showing amount of Galena over time, it shows the partial dissolution of Galena Crystal in a formulation comprising EDTANa4:H2O2 blend (20%w / w:20%w / w)) at pH 11. Dissolution stops after about one hour due to the degradation of the EDTANa4 caused by the hydrogen peroxide.

[0117] Figure 12 is an illustration of the primary degradation products of EDTA which consist of aminopolycarboxylic acid structures obtained by cleavage of one acetic acid group. The degradation of EDTA and DTPA leads to the formation of ethylenediaminetriacetic acid (1 ,1 ,4-EDTA) and to the two isomers of diethylenetriaminetetraacetic acid (1 ,1 ,4,7-DTTA and 1 ,1 ,7,7-DTTA), respectively. In all of the degradation pathways, glyoxylic acid is formed. Under oxygen-rich conditions, glyoxylic acid is further oxidized to oxalic acid.

[0118] Whilst the oxidation of lead sulphide to lead thiosulphate appears to be the most attractive option in terms of converting an insoluble mineral to a more water soluble one, it may have the disadvantage of using a chelating agent to sequester the lead ions, that the chelating agent itself is not stable in the oxidising environment that allows the conversion of lead sulphide to lead thiosulphate.

[0119] Example 6 Zinc Sulphide

[0120] The insoluble deposit in this example is zinc sulphide which is a mineral scale which may be deposited on production tubing and topsides oil production vessels which can reduce oil flow and the efficiency of oil production operations. It sometimes co-deposits with lead sulphide in subsurface safety valves making them inoperable. Zinc Sulphide AR Grade powder 0.3g was added to 30mls of Formulation comprising 35%w / w solution of Ammonium Acetate in combination with 10%w / w hydrogen peroxide at 20°C. As shown in Figure 13A the zinc sulphide initially formed a milky white suspension of particles the dissolver gradually became less and less opaque over 2 hours until it formed a clear colourless solution as the zinc sulphide was oxidised to zinc sulphate which may then react with the ammonium salt to form zinc acetate (Figure 13B).

[0121] The composition according to an embodiment of the invention is comprised of two essential active ingredients; an oxidising agent configured to convert the exposed surfaces on the solid / liquid deposit to an oxidised solid form that has a much greater solubility, and a dissolver agent configured to dissolve the exposed oxidised solids. The two components of the formulation significantly, and surprisingly, improves the ability to dissolve mercury, lead and metal sulphide solid material. The oxidising agent and dissolver agent have a cyclic relationship. The oxidising agent oxidises exposed surfaces of the solid / liquid material, the dissolver agent dissolves the oxidised surfaces which in turn exposes fresh surfaces on the solid / liquid deposit on which the oxidising agent acts. In this way the rate of reaction may be maintained until the solid is fully dissolved.

[0122] The composition according to an embodiment of the invention can quickly and efficiently dissolve toxic metals and metal sulphides and their radioisotopes. As a result, the treatment composition can be used in various applications to decontaminate surfaces and remove harmful metals and metal sulphide including the oil and nuclear industries. The composition has the advantage over physical removal techniques in that it can work remotely, safely and is able to access the smallest most restricted inaccessible contaminated surfaces such as present in small bore pipes, complex pipe bend configurations and corroded and pitted areas of steel surfaces which may harbour hazardous contaminants trapped in the pores and fissures in the near surface of pipes, equipment and vessels involved in oil and gas production and processing.

[0123] The invention may provide compositions and method of use for the dissolution of at least one material comprising mercury, lead and / or metal sulphide, the composition comprising an oxidising agent configured to convert at least part of the at least one material to an oxidised solid, and a dissolver agent to dissolve the oxidised solid. The method comprising contacting the composition with the at least one material. The composition according to an embodiment of the invention may be capable of dissolving deposits which are virtually insoluble in both water and conventional mineral acids or alkalis used to dissolve other deposits. The composition according to an embodiment of the invention may convert an insoluble deposit into a form that has a much greater solubility and expose them to a dissolver agent capable of efficiently dissolving the oxidized form of the deposit. The composition according to an embodiment of the invention may comprise two chemicals (an oxidising agent and a dissolver agent) that act synergistically to convert and then dissolve the metal contaminant in a single stage soak operation to solubilize the deposit and thereby decontaminate surfaces contaminated by metal or metal sulphides.

[0124] Throughout the specification, unless the context demands otherwise, the terms 'comprise' or 'include', or variations such as 'comprises' or 'comprising', 'includes' or 'including' will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

[0125] The foregoing description of the invention has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the invention.

Claims

Claims1. A composition for the dissolution of at least one material comprising mercury, lead and / or metal sulphide, the composition comprising an oxidising agent configured to convert at least part of the at least one material to an oxidised solid; and a dissolver agent to dissolve the oxidised solid.

2. The composition according claim 1 wherein the oxidising agent is selected from the group comprising hydrogen peroxide, inorganic peroxides, halogens, nitric acid, potassium chlorate, sulfuric acid, peroxydisulfuric acid, hypochlorite, chlorite, chlorate and perchlorate.

3. The composition according to claim 1 or 2 wherein the metal sulphide is lead sulphide or zinc sulphide.

4. The composition according to any preceding claim wherein the dissolver agent comprises carboxylic acid and / or a salt of a carboxylic acid.

5. The composition according to any preceding claim wherein the dissolver agent comprises at least one chelating agent selected from the group comprising ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), diethylenetriaminepentaacetic acid (DTPA),glucoheptonic acid and gluconic acid and their alkali metal and ammonium salts.

6. The composition according to any preceding claim wherein the composition comprises about 10% to about 40% oxidising agent by weight.

7. The composition according to any preceding claim wherein the composition comprises about 5% to about 50% dissolver agent by weight.

8. The composition according to any preceding claim wherein the composition comprises about 30% to about 85% w / w water.The composition according to any preceding claim wherein the composition is an acidic pH composition comprising hydrogen peroxide and at least one carboxylic acid. The composition according to any preceding claim wherein the composition is an alkali pH composition comprising hydrogen peroxide and at least one carboxylate salt. The composition according to any preceding claim wherein the composition is a neutral pH composition comprising hydrogen peroxide and at least one carboxylate salt. The composition according to any preceding claim wherein the composition comprises lactic acid, hydrogen peroxide and water. The composition according to any of claims 1 to 11 wherein the composition comprises ammonium acetate, hydrogen peroxide and water. The composition according to any of claims 1 to 11 wherein the composition comprises acetic acid, hydrogen peroxide and water. A method of dissolving at least one material comprising mercury, lead and / or metal sulphide, the method comprising providing a composition comprising an oxidising agent configured to convert at least part of the material to an oxidised solid; and a dissolver agent configured to dissolve the oxidised solid; contacting the at least one material with the composition. The method according to claim 15 wherein the oxidising agent is configured to convert an outer surface of the material to an oxidised solid and wherein the dissolver agent is configured to dissolve the outer surface. The method according to claim 15 or 16 wherein the oxidising agent is selected from the group comprising hydrogen peroxide, inorganic peroxides, halogens, nitric acid, potassium chlorate, sulfuric acid, peroxydisulfuric acid, hypochlorite, chlorite, chlorate and perchlorate.The method according to any of claims 15 to 17 wherein the dissolver agent comprises carboxylic acid and / or a salt of a carboxylic acid. The method according to any of claims 15 to 18 wherein the composition comprises hydrogen peroxide and water and at least one of lactic acid, ammonium acetate or acetic acid. The method according to any of claims 15 to 19 comprising contacting the material with the composition for a period of time between 15 mins and 12 hours. The method according to any of claims 15 to 20 comprising contacting the material with the composition at a temperature in the range of 20°C to 90°C. The method according to any of claims 15 to 21 wherein the at least one material is a deposit or scale. The method according to any of claims 15 to 22 comprising contacting or spraying the composition on, in or through pipes, pipelines, pipeline joints, seals and gaskets, pipeline equipment, refinery equipment, refinery pipework, vessels and / or processing equipment involved in oil and gas operations, nuclear reactors and / or lead shielding materials. The method according to any of claims 15 to 23 wherein the method comprises replacing spent composition with fresh dissolver agent and / or oxidising agent. The method according to any of claims 15 to 24 comprising separating the at least one material comprising mercury, lead and / or metal sulphide contaminated with radioactive material from the radioactive material by dissolving the mercury, lead and / or metal sulphide materials and separating the insoluble radioactive material from the soluble material.

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