Mechanism Of Oxidative Leaching Of Uranium Ore In Sandstone By Ozone(Oxygen) Micro-nano Bubbles

In-situ leaching of uranium has become an important uranium mining and smelting method in our country,mainly including the acid leaching process and alkaline leaching process,and the CO₂+O₂is derived from the conventional alkaline leaching process.The acid leaching process generally uses sulfuric acid,which is widely used because of its low price,convenient transportation,less corrosiveness,timely subsequent treatment of the leaching solution,and non-volatile.However,the leaching process often needs to add an oxidant,which is easy to introduce other heavy metal ions to cause secondary pollution.Although the CO₂+O₂leaching process has been industrially applied in many uranium mining enterprises in our country,the production practice over the years has shown that there are still the following problems in the process of in-situ leaching uranium:（1）The mechanism of oxygen leaching of uranium is unclear.（2）The oxygen solubility is low,the utilization rate is low,the oxidation rate is slow,and the oxidation capacity is not strong.（3）Therefore,this method consumes a large quantity of oxygen and has a high raw material cost（30 to 50%）.（4）The large particle size of the pressurized dissolved oxygen bubbles is likely to cause gas blockage in the ore bed,reduce the permeability of the ore bed,and reduce the amount of drilling fluid pumping and injection.These problems have always plagued engineers and technicians.It is of great significance to discuss these problems,which include the mechanism of oxidative leaching of uranium under the conditions of in-situ leaching of uranium,reducing bubble size,increasing oxygen solubility,improving oxygen utilization,reducing oxygen consumption,reducing production cost,and looking for an efficient and green oxidant,that is closely watched and urgently solved by in-situ leaching uranium mining enterprises.Therefore,after analyzing the mineralogy of sandstone uranium ore and the characteristics of micro-nano bubbles,this paper takes micro-nano bubbles,pyrite,and sandstone uranium ore as the research objects and proposes to use a micro-nano generator to generate micro-nano bubbles instead of the existing pressurized dissolved oxygen process utilizes the characteristics of oxygen micro-nano bubbles and ozone micro-nano bubbles（OMNBs）to study its dissolution characteristics,mass transfer characteristics,and the mechanism of oxidative leaching of uranium.The main contents and conclusions of this work are as follows:1.Research on process mineralogy and conventional exploratory leaching test of sandstone uranium ore.By collecting core samples of sandstone uranium ore from in-situ leaching uranium mines,the rock and mineral identification of the cores was carried out;For the sandstone uranium ore used in this experiment,acid leaching,alkaline leaching,and CO₂+O₂pressurization routines were first carried out without micro-nano bubbles.The results show that:（1）The content of Si O₂in the ore is about 80%,and the content of Ca O and Mg O is low,which belongs to the silicate type ore;the tetravalent uranium in the ore accounts for about 52.74%,and the ore grade is positively correlated with the content of pyrite and organic matter.（2）The acid leaching effect of the ore is good with adding oxidant 5g/L sulfuric acid solution stirring and leaching.The leaching rate of the liquid meter is 80.05%.（3）The alkali leaching effect of ore is poor.Under various enhanced leaching conditions such as high concentration of ammonium bicarbonate,high concentration of oxidant,and stirring leaching for 72 hours,the maximum leaching rate of the liquid meter is only 69.99%.（4）The leaching effect of CO₂+O₂pressure stirring leaching is not good,and the highest uranium leaching rate is only 26.33%,which may be due to insufficient HCO₃^-concentration and dissolved oxygen concentration.2.Experimental research on micro-nano bubbles and ferrous oxide characteristics.The basic properties such as Zeta potential,particle size distribution,and dissolved oxygen were characterized and studied;The effect of different gas sources,initial p H,initial ferrous concentration,ventilation flow,and ozone generation rate on its oxidation effect was studied through the pre-experiment of ferrous ions in the oxidation solution of micro-nano bubbles.The following main conclusions were obtained:（1）The Zeta potential value of the ozone micro-nano bubble was the highest,followed by oxygen,air,and carbon dioxide;the particle size distribution of the micro-nano bubble was unimodal peak size was between 10 and 100μm.（2）Micro-nano bubbles can rapidly increase the dissolved oxygen in water through pressurized dissolution.Micro-nano bubbles with ozone as the gas source can make the dissolved oxygen in water reach about 40mg/L within 10 minutes,and the dissolved ozone concentration can reach up to 12mg/L or so.（3）The oxidation reaction of ferrous iron in an aqueous medium is very effective based on the continuous aeration of ozone micro-nano bubbles.The increase in ventilation flow and ozone generation rate increased the concentration of dissolved ozone in the aqueous phase and promoted the oxidation of Fe（II）.When the p H value is 3-6,the removal rate of Fe（Ⅱ）can reach100%.The higher the initial p H value of the solution,the faster the reaction rate.（4）The oxidation reaction of Fe（Ⅱ）with ozone conforms to second-order kinetics.The overall reaction rate constant and volumetric mass transfer coefficient of ozone increased slightly with increasing p H.In contrast,the reactor’s steady-state dissolved ozone concentration decreased with increasing p H.3.Study on the mechanism of oxidative leaching of sandstone uranium ore by ozone micro-nano bubbles.Pyrite is often used as an associated ore of sandstone uranium ore and is closely related to the uranium leaching process.Therefore,the oxidation test of single mineral pyrite was first carried out using the micro-nano bubble technology to explore pyrite’s ozone micro-nano bubble oxidation mechanism.Under the conditions that the initial p H of the solution is 1～3,the ventilation flow rate is 1～3L/min,the ozone generation rate is 0.55～2.22mg/s,and the initial pyrite concentration is 0.1～5.0g/L,the stirring oxidation is carried out for 60min.experiment.The results showed that:（1）Compared with the oxygen source and conventional aeration methods,the OMNBs aeration method significantly increases the efficiency by 35.2%and33.1%,respectively.（2）The oxidation efficiency of pyrite can reach57.6%at an initial p H value of 1,an initial pyrite concentration of500mg/L,an ozone generation rate of 1.67mg/s,and an agitation of 500rpm for 1h by OMNBs technology.（3）Mn（Ⅵ）increased the oxidation efficiency of pyrite by 21.7%,but Fe（Ⅲ）reduced the oxidation efficiency by 14.4%,compared with the OMNBs without other co-oxidants.SEM and XPS analysis results show that the high Fe（Ⅲ）concentration in the solution causes the formation of Fe（Ⅲ）-O film on the surface of the ore,which inhibits the oxidation rate of pyrite to a certain extent.4.Mechanism of Oxidative Leaching of Uranium Ore in Sandstone by Ozone Micro-Nano Bubble.The effect of micro-nano bubble solution on the oxidative leaching of sandstone uranium ore the leaching mechanism was studied.The sandstone uranium ore and the UO₂were used on batch and continuous flow tests.The oxidation efficiency and rate of UO₂and sandstone uranium ore oxidation by ozone micro-nano bubble were studied and evaluated.XRD,SEM,etc.,were used to analyze and characterize the sandstone uranium ore surface and phase composition before and after the reaction under different conditions and explore its oxidation leaching mechanism.The conclusion is as follows:（1）Compared with ozone micro bubbles,OMNBs increased the oxidation rate by 12 times under p H 1,and the leaching efficiency reached more than 90%.（2）The oxidation efficiency of sandstone uranium ore and UO₂under different p H conditions was evaluated through a pilot treatment system using OMNBs batches and continuous flow.The addition of sulfuric acid and ozone improved the leaching rate of uranium.For sandstone uranium ore and UO₂,a higher leaching efficiency can be achieved after OMNBs treatment at p H 1 and 6.8 for 2h.However,for UO₂,the leaching efficiency can reach about 74.44%after 2h treatment with p H 3 OMNBs,and UO₂was easier to be leached.（3）The continuous test flow verifies the feasibility of large-scale tests and provides a new method for CO₂+O₂in situ uranium leaching under atmospheric pressure.（4）The oxidative leaching of uranium in sandstone uranium ore mainly relies on ozone oxidation,and hydroxyl radicals had little effect on the oxidative leaching of uranium.The analysis showed that OMNBs treatment could significantly destroy gangue minerals in sandstone uranium ore and improve the uranium leaching rate.（5）Applying pyrite to sandstone uranium ore for ozone micro-nano bubble leaching under acidic conditions suggests that Fe（III）present in the leaching solutionpromotes uranium dissolution due to ozonation and chemical dissolution of pyrite.In summary,using OMNBs to leach sandstone uranium ore enhances the oxidation effect,improves the oxidation rate,can effectively reduce the pollution of external chemical oxidants in in-situ leaching of uranium,and can effectively improve the in-situ leaching of mine groundwater.OMNBs oxidation leaching mechanism of sandstone uranium ore provides a theoretical basis and technical principle for the sustainable development of in-situ leaching uranium mining technology.