Method of removing NORM from contaminated material

Abstract

The invention provides a system and method of treating material from a production waste pit contaminated with naturally occurring radioactive material (NORM). The method comprises contacting NORM cont

Description

The present invention relates to methods for treating materials contaminated with naturally occurring radioactive material (NORM), in particular to methods for removing NORM from contaminated sand. Aspects of the invention relate to a decontamination method of NORM contaminated sand from hydrocarbon production waste pits. Background to the invention Naturally Occurring Radioactive Materials (NORM) are present at varying levels in the earths crust as a result of the decay of heavy elements produced by cosmic processes. During hydrocarbon production processes elevated NORM concentrations have been detected in waste streams including produced water, scales, and sludges. Produced water from oil reservoirs often contain naturally occurring radioisotopes such as radium that have been leached from minerals present in the reservoir rock formations. The dissolved radioisotopes are transported to the surface in the produced water waste stream. The dissolved radioisotopes either remain in solution in the produced water or under proper conditions coprecipitate with barium, strontium, lead or calcium to form water-insoluble mineral scale. Sludges can form composed of dissolved solids which precipitate from the produced water as its temperature and pressure change. Sludge generally consists of oily, loose material often containing sand and NORM precipitated scales. As the produced water contacts material such as sand the surface of the material can provide nucleation sites for the formation and adherence of the scale onto the surface as a NORM mineral coating. In previous times large waste pits have been created for the storage or disposal of waste streams and sludge. However, in recent times in accordance with increasingly strict environmental regulations, treatment of NORM contaminated waste streams and sludge stored in pits is reguired to reduce the risk of contamination of the surrounding pit area, as well as decrease the overall waste volume. An operator is reguired to return decontaminated clean sand to the pit by removing NORM contaminants from the sand at considerable cost, before the pit site can be closed. Summary of the invention It is an object of the present invention to obviate or at least mitigate the foregoing disadvantages of NORM decontamination methods. It is another object of an aspect of the present invention to provide a method of removing NORM from materials such as sand. It is a further object of an aspect of the present invention to provide a treatment for waste pit sand to dissolve NORM scale. Further aims of the invention will become apparent from the following description. According to a first aspect of the present invention there is provided a method for treating material from a production waste pit contaminated with naturally occurring radioactive material (NORM), the method comprising the steps of: contacting NORM contaminated material with a first solution comprising an alkali metal carbonate and / or alkali metal bicarbonate to form material contaminated with a soluble NORM salt; contacting the material contaminated with soluble NORM salt with a second solution comprising at least one acid to dissolve the soluble NORM salt; and collecting the treated material. By contacting NORM contaminated material with the first solution comprising an alkali metal carbonate and / or alkali metal bicarbonate the NORM is converted to a soluble NORM salt. By contacting the material contaminated with soluble NORM salt with a second solution comprising at least one acid the soluble NORM salt is dissolved. This allows removal of the NORM free treated material and optionally the recovery of the NORM. The material contaminated with NORM may be material from sand, soil, mining cuttings and / or mining tailings. The material contaminated with NORM may be any material from a production waste pit. The material may be contaminated with NORM scale. The NORM scale may be a water, acid and / or an alkali insoluble NORM scale. The material contaminated with soluble NORM salt may be a water, acid and / or an alkali soluble NORM salt. The method may comprise exposing or soaking the NORM contaminated scale in the first solution. Preferably the first solution is a converting solution. The method may comprise contacting the NORM-contaminated material with the first solution for between 5 to 60 mins. The temperature of the material and first solution mixture may be in the range of 60°C to 95°C. The method may comprise contacting the NORM-contaminated material with the first solution for 15 mins at 80°C. The converting solution may comprise potassium carbonate. The converting solution may comprise a solution configured to react with sulphate or Sulphide to form a salt that is readily soluble in water, acid and / or alkali solutions. The converting solution may comprise any alkali metal carbonate and / or alkali metal bicarbonate. The concentration of converting solution used may be chosen based on the amount of NORM associated with the contaminated material. The amount of converting solution may be chosen based on the amount of fluid required to create a slurry with the material. The solution or slurry may comprise approximately 25% by weight converting solution. The second solution may comprise at least one mineral acid or organic acid. The at least one acid may be hydrochloric acid nitric acid and / or acetic acid. The method may comprise contacting the material contaminated with soluble NORM salt with the second solution for between 5 to 60 mins. The temperature of the material to be treated and second solution mixture may be ambient temperature. The temperature of the material to be treated and second solution mixture may be in the range of 5°C to 40°C. The method may comprise contacting the material contaminated with soluble NORM salt with the second solution for 15 mins at 20°C. The second solution may be a dissolver solution. The ratio of material contaminated with soluble NORM salt to second solution may be in the range of 10:1 to 1:1. The ratio of material contaminated with soluble NORM salt to second solution may be 2:1. The method may comprise dissolving calcium carbonate present using the second solution. The method may comprise removing one or more non-radioactive materials from the material. The one or more non-radioactive materials may be at least one hydrocarbon. The one or more non-radioactive materials may be at least one hydrocarbon fluid or hydrocarbon material. The method may comprise removing at least one hydrocarbon from the material. The method may comprise a pre-treating step to remove at least one hydrocarbon from the material. The at least one hydrocarbon may be removed using water heated to between 40-60°C, a surfactant and / or a solvent treatment. The method may comprise removing one or more non-radioactive materials from the NORM contaminated material before, after and / or during contacting NORM contaminated material with the first solution. The method may comprise washing the contaminated material before contacting NORM contaminated material with a first solution. The method may comprise washing the contaminated material before contacting the soluble NORM salt with the second solution. The method may comprise dissolving any calcium carbonate in the second solution. The method may comprise recovering a solid NORM. The method may comprise precipitating NORM and other solids from spent second solution. The method may comprise precipitating NORM and other solids by contacting spent first solution with spent second solution. The NORM may be selected from the group comprising barium, strontium, lead or radium and / or a combination thereof. The NORM may be in the form of barium sulphate, strontium sulphate, radium sulphate and / or lead sulphate and / or a combination thereof. The NORM may be in the form of barium sulphide, strontium sulphide, radium sulphide and / or lead sulphide and / or a combination thereof. According to a second aspect of the present invention there is provided a method of treating NORM contaminated scale, the method comprising: treating the NORM contaminated scale with a converting solution to convert the NORM contaminated scale to a soluble NORM salt; treating the soluble NORM salt with a second solution to dissolve the soluble NORM salt. The NORM contaminated scale may be a water, acid and / or an alkali insoluble NORM scale. The soluble NORM salt may be a water, acid and / or an alkali soluble NORM salt. The NORM contaminated scale may be treated with a converting solution by exposing or soaking the NORM contaminated scale in the converting solution. The converting solution may comprise any alkali metal carbonate and / or alkali metal bicarbonate. The converting solution may comprise a solution configured to react with sulphate to form a salt that is readily soluble in water, acid and / or alkali solutions. The converting solution may comprise potassium carbonate. The concentration of converting solution used may be chosen based on the amount of NORM contaminated scale. The amount of converting solution may be chosen based on the amount of fluid required to create a slurry with the NORM contaminated scale. The solution or slurry may be approximately 25% by weight converting solution. The second solution may comprise at least one acid. The second solution may comprise at least one mineral acid or organic acid. The at least one acid may be hydrochloric acid, nitric acid and / or acetic acid. The method may comprise contacting the sand contaminated with soluble NORM salt with the second solution for between 5 to 60 mins. The temperature of the scale and second solution mixture may be ambient temperature. The temperature of the scale and second solution mixture may be in the range of 5°C to 40°C. The method may comprise contacting the scale contaminated with soluble NORM salt with the second solution for 15 mins at 20°C. The second solution may be a dissolver solution. The ratio of sand contaminated with soluble NORM salt to second solution may be in the range of 10:1 to 1:1. The ratio of scale contaminated with soluble NORM salt to second solution may be 2:1. 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. According to a third aspect of the present invention there is provided a method of treating NORM scale contaminated sand from a production waste pit, the method comprising: converting insoluble NORM scale on the contaminated sand to a soluble NORM salt using a converting solution; dissolving the soluble NORM salt on the contaminated sand using a dissolver solution. The insoluble NORM scale may be a water, acid and / or an alkali insoluble NORM scale. The soluble NORM salt may be a water, acid and / or an alkali soluble NORM salt. The converting solution may comprise potassium carbonate. The converting solution may comprise a solution which reacts with sulphate or sulphide to form a salt that is readily soluble in water, acid and / or alkali solutions. The converting solution may comprise any alkali metal carbonate and / or bicarbonate. The concentration of converting solution used may be chosen based on the amount of NORM scale associated with the contaminated sand. The amount of converting solution may be chosen based on the amount of fluid required to create a slurry with the sand. The solution or slurry may be approximately 25% by weight converting solution. The dissolver solution may comprise at least one mineral acid or organic acid. The dissolver solution may comprise hydrochloric acid. The method may comprise washing the contaminated sand. The method may comprise collecting the decontaminated sand. The method may comprise pre-treating the contaminated sand to remove one or more non-radioactive materials. The one or more non-radioactive materials may be a hydrocarbon. 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. According to a fourth aspect of the present invention there is provided a system for treating naturally occurring radioactive material (NORM) contaminated sand from a production waste pit, the system comprising: a first vessel configured to receive the sand, wherein the sand and a first solution comprising an alkali metal carbonate and / or alkali metal bicarbonate are reacted within the first vessel to form sand contaminated with a soluble NORM salt; a second vessel configured to receive the sand contaminated with a soluble NORM salt, wherein the sand contaminated with a soluble NORM salt and a second solution comprising an at least one acid is reacted within the second vessel to dissolve the soluble NORM salt. The system may comprise a first dosing pump for adding the first solution to the first vessel. The system may comprise a second dosing pump for adding the second solution to the second vessel. The system may comprise a second dosing pump for adding the at least one acid to the second vessel. The system may comprise a hydrocarbon removal stage. The hydrocarbon removal stage may comprise a hot water and / or a chemical wash system to remove hydrocarbon from the sand. The system may comprise at least one screen or shaker configured to separate the sand and the saturated spent first solution from the first vessel. The at least one screen or shaker may be configured to separate the sand and the saturated spent second solution from the second vessel. The system may comprise a NORM recovery stage. The NORM recovery stage may comprise a vessel configured to receive saturated spent second solution wherein the saturated spent second and saturated spent first solution may be reacted within the first vessel to precipitate the NORM. The precipitated NORM may be in the form of NORM sulphate or NORM sulphide. The precipitated NORM may be in the form of barium sulphate, strontium sulphate, lead sulphate and / or radium sulphate. The precipitated NORM may be in the form of sulphide salts of barium, strontium, radium and / or lead. The system may comprise at least one filter configured to remove suspended solids and isolate the NORM for disposal. The at least one filter may be a bank of parallel filters . The at least one filter may be a non-regenerative filter. 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. According to a fifth aspect of the present invention there is provided a method for treating naturally occurring radioactive material (NORM) contaminated sand from a production waste pit, the method comprising the steps of: contacting NORM contaminated sand with a first solution comprising an alkali metal carbonate and / or alkali metal bicarbonate to form sand contaminated with a soluble NORM salt and remove at least one hydrocarbon component from the sand; contacting the sand contaminated with soluble NORM salt with a second solution comprising at least one acid to dissolve the soluble NORM salt; and collecting the treated sand. 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. According to a sixth aspect of the present invention there is provided a method for treating material contaminated with naturally occurring radioactive material (NORM), the method comprising the steps of: contacting NORM contaminated material with a first solution comprising an alkali metal carbonate and / or alkali metal bicarbonate to form material contaminated with a soluble NORM salt; contacting the material contaminated with soluble NORM salt with a second solution comprising at least one acid to dissolve the soluble NORM salt; and collecting the treated material. The material contaminated with NORM may be sand, soil, mining cutting and / or mining tailings. The material contaminated with NORM may be from a production waste pit. 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. According to a seventh aspect of the present invention there is provided a system for treating naturally occurring radioactive material (NORM) contaminated material from a production waste pit, the system comprising: a first vessel configured to receive the contaminated material, a first solution comprising alkali metal carbonate and / or alkali metal bicarbonate; a second vessel configured to receive the material contaminated with a soluble NORM salt; a second solution comprising an at least one acid; wherein the contaminated material and the first solution comprising an alkali metal carbonate and / or alkali metal bicarbonate are reacted within the first vessel to form material contaminated with a soluble NORM salt; wherein the material contaminated with a soluble NORM salt and the second solution are reacted within the second vessel to dissolve the soluble NORM salt. 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. Brief description of the drawings There will now be described, by way of example only, various embodiments of the invention with reference to the drawings, of which: Figure 1 is an enlarged view of a sand grain treated with a method according to an embodiment of the invention; and Figure 2 is a flow diagram of the method according to an embodiment of the invention. Description of the preferred embodiments Figure 1 shows a method 10 of removing NORM scale from sand. For clarity, a single sand grain 11 is shown coated in a layer of NORM scale 12. Figure 1 shows an optional step 20 of the method shown in dotted box 14 where the sand grain 11 has an outer layer of hydrocarbon 16. The hydrocarbon contamination is present at the surface and near-surface of the sand waste pit whilst the NORM-contaminated sand occurs in layers below the surface where the sand is in contact with produced water. This stratified distribution of contamination simply reflects the fact that hydrocarbon floats on water. The nature of the hydrocarbon contamination depends on the reservoir of its origin and how it has been affected by exposure to the sun. The hydrocarbons are likely to contain crude oil together with asphaltenes, waxes and naphthenates and when exposed to the heat of the desert sun these components degrade and when the lighter ends evaporate, the remaining hydrocarbons become partially solidified or greasy resulting in a black or yellow hydrocarbon crust that can be more or less fluid depending on the season and daytime temperature. The hydrocarbon can be removed using a combination of cleaning methods. In this example using water heated to between 40-60°C, optionally combined with surfactant and / or solvent treatment depending on the nature of the hydrocarbon contamination. In this example, the optional step 20, to remove the hydrocarbon component 16 the sand grain is washed in-water at 60°C with a surfactant to remove the hydrocarbon component from the NORM-contaminated sand. At step 22, the NORM-contaminated sand grain 11 is soaked in a first solution “A” to convert the NORM scale 12 to a soluble NORM layer 18. The first solution “A” is a converting solution. The converting solution may be a solution which reacts with sulphate to form a salt that is readily soluble in water, acid and / or alkali solutions. The converting solution may be any alkali metal carbonate and / or bicarbonate. In this example the first solution “A” is Potassium Carbonate solution. The NORM-contaminated sand grain 11 is soaked in the Potassium Carbonate solution for between 15 to 30 mins at 80°C. At step 24, the sand grain 11 coated in converted NORM is soaked in a second solution “B” to dissolve the converted NORM scale. The second solution “B” is a dissolver solution. The dissolver solution may be a solution which dissolves the converted NORM such as a mineral acid or organic acid. In this example the second solution “B” is hydrochloric acid. The NORM-contaminated sand grain 11 is soaked in hydrochloric acid for between 15 to 30 mins at 20°C until the converted NORM scale is dissolved. This leaves clean sand grain 11 as shown in Figure 1. Figure 2 is a flow diagram of the method to remove NORM from sand excavated from a pit. In a first example Radium Sulphate is used as an example of a radioactive mineral responsible for NORM contamination of sand where the Radium is present as Ra-226. It will be appreciated that this is one example and that other radioisotopes of Radium, Barium, Lead and Strontium may also (or alternatively) be present in the NORM scale and will be required to be removed alongside the Radium, such as Ra-226 present as Radium Sulphate in order to decontaminate the sand. The different stages of the method 100 of decontaminating sand can be described in reference to Figure 2 as follows: A first optional process 160 of the method shown in dashed box “A” is to treat sand contaminated with hydrocarbon components 116. Waste pits can be considered as consisting of stratified layers offering different forms of contamination. Where hydrocarbon and NORM-containing produced waters have been discharged into the pits, the surface and upper layers extending down to about a metre, are usually primarily contaminated with hydrocarbon and the lower layers of sand typically extending to a depth of about three metres may be in contact with produced waters resulting in NORM contamination of these lower layers. The hydrocarbon may be removed in step 162 using a combination of cleaning methods such as water heated to 40-60°C optionally combined with surfactant and / or solvent treatment depending on the nature of the hydrocarbon contamination. In this example, to remove the hydrocarbon component the sand grain is washed in-water at 60°C with a surfactant to remove the hydrocarbon component from the NORM-contaminated sand. The removed hydrocarbon and water may be recovered as shown in Step 164. Optionally, an oil-water separation phase may be used to clean the wash water and allow it to be recycled through the system, thereby minimizing the water consumption and wastewater volume. If the NORM Contaminated Sand is not contaminated with a hydrocarbon component, then the process 160 is not required. The conversion of NORM scale is achieved by reacting NORM contaminated sand with a converting solution of alkali metal carbonate salt at elevated temperature of between 60°C 95°C. In this example the temperature is maintained at approximately 80°C. In many locations the NORM contaminated sulphate scale comprises a mixed scale containing Barium Sulphate, Strontium Sulphate and Radium Sulphate. These individual mineral scales and different mixtures of these scales react with the converting solution containing carbonate ion for instance to form in this example Barium Carbonate, Strontium Carbonate and Radium Carbonate solids with Potassium Sulphate in solution formed as a by-product of the reaction. In this example shown in Figure 2, the NORM Contaminated Sand 110 present in waste pits consists of sulphate mineral scale contaminated with Radium 226 in the form of a Radium Sulphate scale. In step 112 the insoluble NORM Sulphate, Radium Sulphate, is converted into a soluble form, Radium Carbonate, at the solid-liquid interface at the scale surface by contacting the NORM contaminated sand with a converting solution 114 which in this example is Potassium Carbonate as shown in Equation 1. Other converting solutions that react with sulphate to form a salt that is readily soluble in water, acid or alkali solutions may be used, including for example any alkali metal carbonate or bicarbonate. The concentration of converting solution used may be chosen based on the amount of NORM scale associated with the contaminated sand. The amount of converting solution may be chosen based on the amount of fluid required to create a slurry with the sand. In some embodiments, the solution is approximately 25% by weight converting solution. The converting solution reacts with the NORM scale converting the sulphate mineral scale to carbonate mineral scale with the formation of Potassium Sulphate in aqueous solution. If the NORM scale deposit forms a thin coating on the sand particles the conversion of sulphate scale to carbonate scale can be entirely converted in a one-stage operation. It will be appreciated that if the scale layer is thicker then the conversion process may need to be repeated after dissolving the converted surface layer to expose a fresh layer of unconverted Radium Sulphate. The rate of conversion is enhanced at elevated temperature. The preferred temperature is in the range of 80-95°C. Once the concentration of dissolved sulphate reaches a point of saturation or nearsaturation, the spent converting solution 114a saturated with sulphate ions is drained from the NORM sand and pumped to storage tank in step 124. The sand is water washed in step 125 to remove traces of chemical and dissolved sulphate ion associated with it resulting from the conversion reaction leaving converted NORM contaminated sand in step 126. The cleaned and water washed sand from the conversion process is directed to the NORM dissolution process. In step 128 the converted NORM Scale, Radium carbonate, is mixed with an acid 129 to dissolve the NORM scale. This stage of the process removes the NORM contamination from the sand. The NORM dissolution step utilizes the acid to solubilize the NORM which can then be separated from the sand particles. In this example Hydrochloric acid is used to form an aqueous solution of Radium Chloride salt. Carbon dioxide gas is liberated as the reaction proceeds as shown in (Equation 2). The dissolution is carried out at ambient temperature. The acid solution gradually becomes saturated with Radium Chloride as the carbonate minerals are dissolved. The acid can be re-used in the process until saturated. The ratio of dissolver to sand may be 2:1. In some embodiments, the ratio may be more than 2:1 dissolver to sand. An agitator may be used to help mix the dissolver and sand. The reaction time required will be determined by the level of NORM contamination of the sand and the size of any NORM scale particles, not adhering to sand grains. The reaction time, being the time required to dissolve the NORM will typically be less than 1 hour at 20C. Typically the reaction time ranges between 10 minutes and 60 minutes. Throughout the reaction, the mixture may be continuously agitated and pumped to circulate and optimize contact between the acid dissolver and the NORM-coated sand particles and aid in the liberation of carbon dioxide gas generated as a by-product of the reaction to avoid areas within the bulk sand where gas could become trapped preventing efficient contact between the dissolver and the NORM scale. Optionally a secondary reaction as shown in Equation 3, may occur between the sand particles and the acid dissolver if there are non-radioactive acid-soluble minerals present in sand such as grains of calcite which are usually present alongside grains of Silica sand (SiO2). The calcite is calcium carbonate which formed from the erosion of corals and seashells over millions of years. CaCO3(s) + 2HCI CaCI2+ H2O + CO2(g) (Equation 3) The spent acid solution 129a contains the radioactive metal ions, in this case Ra-226 is drained from the sand in step 130. The sand is water washed in step 132 to remove traces of radioactive metal ions and acid solution. The treated clean sand 134 may be monitored using a radiation monitor to determine whether the sand is fully decontaminated for free release to backfill the pit site or whether another cycle of conversion and acid dissolution is required. The spent converting solution 114a contains dissolved sulphate ions and the spent acid solution 129a contains dissolved NORM metal radioisotopes. The spent acid solution 129a could be disposed of by reinjection into the formation, where there is an injection well that can be used for disposal purposes. Additionally or alternatively, an optional NORM precipitation process 140 shown as dashed box “B” in Figure 2 may be performed to remove the dissolved NORM material from the dissolver solution as a solid waste for disposal. The spent acid solution 129a containing radioactive metal ions is mixed with the spent converting solution 114a to form a precipitate of Radium Sulphate which can then be isolated by filtration for disposal, as shown in Equation 4. RaCh + CaCh + 2K2SO4 -> RaSO4(s) + CaSO4(s) + 2KCI (Equation 4) The solid sulphate scale precipitates as a fine suspension of NORM particles which settles to the base of a NORM Recovery reactor vessel if left to settle. An agitator may be employed to keep the NORM precipitate in suspension. NORM precipitate suspension may be directed through a filter or bank of parallel filters to remove any suspended solids. Non-regenerative filters may be used to remove suspended solids and isolate the NORM contamination for disposal. The solid Radium Sulphate scale can be isolated as a small volume of NORM solid waste, If the reaction is carried out under acid conditions the formation of calcium carbonate can be prevented and the precipitation of calcium sulphate can be avoided reducing the total mass of waste solids to be disposed of. Water washes of sand at steps 125 and 132 are recommended to allow efficient decontamination to be achieved. The water wash prevents trace sulphate ions recombining with dissolved NORM cations released during treatment with the acid dissolverand partially re-contaminating treated sand. The water used to wash the sand at step 125 and 132 and in optional hydrocarbon removal process 160 may become contaminated. An optional wastewater treatment process 150 shown as dotted box “C” in Figure 2 may be used to treat the contaminated water. To treat the contaminated water from multiple processes, each wastewater stream is pumped into a separation tank. Water will pass under a baffle plate and discharge over a weir into a water trough. Coagulant, flocculant and / or pH adjustment chemicals may be injected into the water as the flow exits the separation tank. The coagulants and flocculants for this process may be any known water treatment coagulants and flocculants, including aluminum sulphate, iron sulphate and poly acrylamide. Flocs are formed and settle down the sloped tank bottom to a suction point where it may be removed. Any floating flocs and residual floating oil may be removed from the surface by a suction tube. This slurry may also be pumped to a separator for dewatering. In a second example the NORM contaminated sand present in waste pits consists of sulphide mineral scale contaminated with Lead 210 in the form of a Lead Sulphide. The method step described in Figure 2 will now be described for this second example. The method to remove Lead-210 NORM from sand excavated from a pit is similar to the method of removing Radium Sulphate scale described above. The method involves the converting and dissolution steps. However, the type of dissolver solution is different. In this second example, the method has the same first optional process 160 of the method shown in dashed box “A” to treat sand contaminated with hydrocarbon components 116. The hydrocarbon may be removed in step 162 using a combination of cleaning methods such as water heated to 40-60°C optionally combined with surfactant and / or solvent treatment depending on the nature of the hydrocarbon contamination. In this example, to remove the hydrocarbon component the sand grain is washed in-water at 60°C with a surfactant to remove the hydrocarbon component from the NORM-contaminated sand. The removed hydrocarbon and water may be recovered as shown in Step 164. Optionally, an oil-water separation phase may be used to clean the wash water and allow it to be recycled through the system, thereby minimizing the water consumption and wastewater volume. If the NORM Contaminated Sand is not contaminated with a hydrocarbon component, then the process 160 is not required. The conversion of Lead 210 NORM scale is achieved by reacting NORM contaminated sand with a converting solution of alkali metal carbonate salt, which in this example is Potassium Carbonate, at elevated temperature of between 60°C to 95°C. In this example the temperature is maintained at approximately 80°C. The converting solution converts the NORM sulphide minerals to a carbonate form of lead-210. The concentration of converting solution used may be chosen based on the amount of NORM scale associated with the contaminated sand. The amount of converting solution may be chosen based on the amount of fluid required to create a slurry with the sand. In some embodiments, the solution is approximately 25% by weight converting solution. The converting solution reacts with the NORM scale converting the sulphide mineral scale to carbonate mineral scale with the formation of Potassium Sulphide in aqueous solution. If the NORM scale deposit forms a thin coating on the sand particles the conversion of lead sulphide scale to lead carbonate scale can be entirely converted in a one-stage operation. It will be appreciated that if the scale layer is thicker, then the conversion process may need to be repeated after dissolving the converted surface layer to expose a fresh layer of unconverted lead sulphide. The rate of conversion is enhanced at elevated temperature. The preferred temperature is in the range of 80-95°C. Once the concentration of dissolved sulphide reaches a point of saturation or nearsaturation, the spent converting solution 114a is drained from the NORM sand and pumped to storage tank in step 124. The sand is water washed in step 125 to remove traces of chemical and dissolved sulphide ion associated with it resulting from the conversion reaction leaving converted NORM contaminated sand in step 126. The cleaned and water washed sand from the conversion process is directed to the NORM dissolution process. In step 128 the converted NORM Scale, lead carbonate, is mixed with a mineral acid or organic acid 129 to dissolve the NORM scale. This stage of the process removes the NORM contamination from the sand. The NORM dissolution step utilizes the acid to solubilize the NORM which can then be separated from the sand particles. In this example nitric acid is used to form an aqueous solution of lead nitrate salt. The dissolution is carried out at ambient temperature. The acid solution gradually becomes saturated. The acid can be re-used in the process until saturated. The sand is water washed in step 132 to remove traces of radioactive lead 210 ions and acid solution. The treated clean sand 134 may be monitored using a radiation monitor to determine whether the sand is fully decontaminated for free release to backfill the pit site or whether another cycle of conversion and acid dissolution is required. As an alternative to nitric acid, organic acids such as acetic acid may be used to react with the lead carbonate to produce soluble lead salts. Optionally, the dissolver solution could comprise an alkaline sequestering agent to avoid the generation of toxic hydrogen sulphide gas. In many locations the NORM contamination may comprise a mixed scale containing a combination of barium sulphate, strontium sulphate, radium sulphate and / or lead sulphide. These individual mineral scales and different mixtures of these scales react with the converting solution containing carbonate ion for instance to form in this example Barium Carbonate, Strontium Carbonate, Radium Carbonate and / or Lead Carbonate. In the above example, the method is described as having an optional hydrocarbon removal process 160 to remove hydrocarbons from the sand before treating the NORM contamination. In another embodiment of the invention rather than use a separate process to remove hydrocarbon from contaminated sand as a pre-treatment process using hot water and / or surfactants, instead the hydrocarbon contaminated sand is treated with a solution comprising converter solution such as Potassium Carbonate which is heated by a heat exchanger to a temperature of around 80C and which in addition to assisting in the removal of hydrocarbon from the contaminated sand also converts the NORM scale from a NORM sulphate or sulphide mineral scale to a NORM carbonate scale. The treatment of hydrocarbon-contaminated sand with converter solution allows the sand to be cleaned of hydrocarbon and converted in a single operation. The opportunity to combine the hydrocarbon removal and NORM conversion steps depends on the nature and extent of the hydrocarbon contaminating the sand. Core samples can be taken to identify different contaminated strata and the nature and extent of contamination over the area of the waste pit. The cleaning process of different layers can be optimized depending on the nature of the contamination. Some layers may be contaminated by both hydrocarbon and NORM scale and require both contaminants to be removed whilst deeper layers of sand may only have been contacted by produced water and have experienced NORM contamination and therefore do not require the hydrocarbon removal process. The most efficient general decontamination approach will target the decontamination of similarly contaminated layers over the area of the waste pit and treat this in the optimum manner depending on the nature of the contaminant or contaminants. The treatment of the pits may be treated by sequentially removing one metre layers of sand from the waste pit and decontaminating sand down to the depth where contamination stops. 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. The invention provides a method of treating NORM contaminated scale. The method comprises the step of treating the NORM contaminated scale with a converting solution to convert the insoluble NORM scale to a soluble NORM scale. The method also comprises treating the soluble NORM contaminated scale with a second solution to dissolve the soluble NORM scale. The present invention according to an embodiment of the invention may provide a method of treating NORM contaminated materials with improved speed and reliability. NORM contamination of sand in waste pits occurs as a thin coating of mineral scale on sand particles. Embodiments of the invention may provide a method of removing the radioactive coating on the sand by converting the NORM coating to a more soluble form and then dissolving the NORM which is a rapid and low cost method. The method may include washing the contaminated sand with a solution to convert the naturally occurring radioactive material to a different mineral form, washing the converted contaminated sand with a dissolver solution and water to remove naturally occurring radioactive material from the sand, recovering the converting solution and dissolver solution from the sand, and collecting the treated decontaminated sand. The method may include pre-treating the contaminated sand to remove hydrocarbon contamination. By providing a method of treating NORM contaminated sand according to an embodiment of the invention the treatment of extensive volumes of NORM contaminated sand may be performed quickly and without large processing plants. Typically, waste pits for the storage or disposal of waste streams and sludge are located in remote areas. The present invention may provide a method which may be conducted in remote areas and without the use of expensive specialised chemicals such as chelating agents which often require complex treatments to recycle the chelating agents The present invention may provide a method of treating NORM contaminated sand without pre-treatment of the sand to remove calcium carbonate. The present invention according to an embodiment of the invention may provide an optimised method with a minimal number of treatment stages and time required to effect each treatment stage. The present invention according to an embodiment of the invention may provide minimal amount of NORM waste produced for disposal. The method may be capable of treating and reusing the water and solutions used throughout the process so that fresh water is not constantly added to the system and contaminated water is not released to the environment. 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 as defined by the appended claims.

Claims

1. A method for treating material from a production waste pit contaminated with naturally occurring radioactive material (NORM), the method comprising the steps of: contacting NORM contaminated material with a first solution comprising an alkali metal carbonate and / or alkali metal bicarbonate to form material contaminated with a soluble NORM salt;contacting the material contaminated with soluble NORM salt with a second solution comprising at least one acid to dissolve the soluble NORM salt; and collecting the treated material.

2. The method according to claim 1 wherein the material contaminated with NORM is material selected from the group comprising sand, soil, mining cuttings and / or mining tailings.

3. The method according to claim 1 or claim 2 wherein the material is contaminated with a water insoluble NORM scale, an acid insoluble NORM scale and / or an alkali insoluble NORM scale.

4. The method according to any preceding claim wherein the material contaminated with soluble NORM salt is a water soluble NORM salt, an acid soluble NORM salt and / or an alkali soluble NORM salt.

5. The method according to any preceding claim comprising exposing or soaking the NORM contaminated scale in the first solution.

6. The method according to any preceding claim comprising contacting the NORM-contaminated material with the first solution for at least 15 mins at 80°C.

7. The method according to any preceding claim wherein the first solution comprises potassium carbonate.

8. The method according to any preceding claim wherein the first solution is configured to react with sulphate or sulphide in the NORM to form a salt that is readily soluble in water, acid and / or alkali solutions.

9. The method according to any preceding claim wherein the second solution comprises at least one mineral acid or organic acid.

10. The method according to any preceding claim wherein the at least one acid is hydrochloric acid, nitric acid and / or acetic acid.

11. The method according to any preceding claim comprising contacting the material contaminated with soluble NORM salt with the second solution for 15 mins at 20°C.

12. The method according to any preceding claim wherein the second solution is a dissolver solution.

13. The method according to any preceding claim wherein the ratio of material contaminated with soluble NORM salt to second solution is in the range of 10:1 to 1:1.

14. The method according to any preceding claim comprising dissolving calcium carbonate present using the second solution.

15. The method according to any preceding claim comprising removing one or more non-radioactive materials from the material.

16. The method according to any preceding claim comprising performing a pre-treating step to remove at least one hydrocarbon from the material.

17. The method according to any preceding claim comprising removing the at least one hydrocarbon using water heated to between 40°C -60°C, a surfactant and / or a solvent treatment.

18. The method according to any preceding claim comprising removing one or more non-radioactive materials from the NORM contaminated material before, after and / or during contacting NORM contaminated material with the first solution.

19. The method according to any preceding claim comprising washing the contaminated material before contacting NORM contaminated material with a first solution.

20. The method according to any preceding claim comprising washing the contaminated material before contacting the soluble NORM salt with the second solution.

21. The method according to any preceding claim comprising precipitating NORM and other solids from spent second solution.

22. The method according to any preceding claim comprising precipitating NORM and other solids by contacting spent first solution with spent second solution.

23. The method according to any preceding claim wherein the NORM is selected from the group comprising barium, strontium, lead or radium and / or a combination thereof.

24. A system for treating naturally occurring radioactive material (NORM) contaminated material from a production waste pit, the system comprising:a first vessel configured to receive the contaminated material,a first solution comprising an alkali metal carbonate and / or alkali metal bicarbonate; a second vessel configured to receive the material contaminated with a soluble NORM salt;a second solution comprising an at least one acid;wherein the contaminated material and the first solution react within the first vesselto form material contaminated with a soluble NORM salt;wherein the material contaminated with a soluble NORM salt and the second solution react within the second vessel to dissolve the soluble NORM salt.

25. The system according to claim 24 comprising a first dosing pump for adding the first solution to the first vessel and / or a second dosing pump for adding the second solution to the second vessel.

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