Migration And Enrichment Of High Concentration Uranium In The Hydrological System Of Gas Hure Salt Lake, Qaidam Basin

Uranium is key for the military industry and the nuclear power industry.Maintaining enough uranium reserves is of great significance to the sustainable and stable development of national security and economy.There is high level concentration uranium in the brine,especially in the Gas Hure Salt Lake(GHSL),which has great value for development and utilizion.Studying the migration and enrichment of uranium in the hypersaline environment is very helpful to exploring the uranium resource.In this thesis,the migration and enrichment of uranium were investigated from the point of view of hydrological system of the Qadam Basin.The samples were collected from the mountains around the GHSL plain: 10 from the Kulamulekesay River(KLMH),4 from the Atetikan River(ATKH),3 from the Alaer River(ALEH),13 from springs,6 from streams,4 from shallow wells(2-5 m),10 from the GHSL,11 from the shallow aquifer(intercrystalline brine,3-5 m),5 from drilling holes(S06,3.67 m;S06,19.7 m;S06,31.7 m;S06,55.5 m;S06,61.0 m),and 5 from the salt field.Moreover,20 rock samples were collected.The aims of this study were to:(1)investigate the hydraulic connections and recharging end-members in this hydrological system by using both the chemical and isotopic methods(?D,?18O,?11?(11)(11)234U/238U);(2)identify the origin of the uranium and water-rock interactions;(3)reveal the hydrogeochemical behaviors for migration and enrichment of uranium in the hydrological system.This work highly benefits the understanding of the theory of uranium behaviors in saline environments,and it also has practical significance for development and exploration of uranium.The main results were shown below:(1)Extensive hydraulic connections existed among the different type waters in the GHSL area,except for the samples(GJJ15-7,GJJ15-10)from the alluvial fan of QMTGM and samples(GJ10-4)from the alluvial fan of YSM.The evidences of the physic-chemical parameters,chemical characters and isotopes suggested that the GHSL brine recharged from the high mountain rivers(KLMH and ATKH)and deep fluid,with each contributing 56.01% and 43.99%,respectively.The recharge elevation of the rivers ranged from 3869 m to 4616 m.(2)The evidences from hydrochemistry and isotope of the profiles showed that the intense water exchange zones were distributed in front of QMTGM;the zones with slow water exchange were distributed in the north of the salt lake plain;and the deep fluid waters were distributed in the zone with very slow water exchange.There were two water flow systems: the local water flow system suggested strong water exchange and was dominated by the HCO3-Na·Ca type;and the regional water flow system showed slow/very slow water exchange and was dominated by the Cl-Na type water.(3)The sources of the elements in GHSL were mainly from rock weathering and leaching,such as silicate(e.g.,granite,quartz,feldspar)from the surrounding mountains,carbonate and evaporite of the overflow area and salt lake plain,and the relative abundance of the carbonate and evaporite are 35.60% and 34.99% in the overflow area and 63.89% and 35.92% in the salt lake plain,respectively.The uranium of the salt lake brine was from the U-bearing rock,such as granite from high mountains;dolomite,calcite,magnesite,gypsum,mirabilite,halite from overflow area and salt lake plain.The uranium in the deep fluid was from silicate and evaporite.The formation of high concentration uranium based on the highly extensive water-rock interaction,including leaching;evaporation,cation exchange and mixing;and the mixing ratios of the end-member were 54.36% and 45.64%,respectively.(4)The migration and enrichment of uranium have obvious zonations,such as oxide leaching zone(OLZ),transition reduction zone(TRZ)and enriched oxidation zone(EOZ).OLZ: strong water exchange was shown,234U/238U?1,mainly leaching process,HCO3-Na·Ca type water,low TDS(<2.0 g/L);In the alkalinity-neutral oxidation environment,the species of uranium mainly consisted of UO2(CO3)34-and UO2(CO3)22-,which promoted uranium migration.The average uranium concentration was 9.5 ?g/L.The TRZ included weak alkalinity-neutral reduction zone(I)and neutral-weak acid reduction zone(II).(I): this zone was distributed in the overflow area,234U/238U=1.1~1.3,principal mixing process,HCO3-Na·Ca type water,TDS<6.0 g/L;under the weak alkalinity-neutral reduction conditions,the uranium species were mainly changed from UO2(CO3)34-to UO2CO3 and UO2(OH)3-,and uranium was reducted.Uranium concentration was 18.81 ?g/L.(II): waters from deep fluid shown very slow water exchange,234U/238U=1.2~1.4,mainly including the mixing and cation exchange processes.Water type was Cl-Na type and Ca2+ rich water with TDS>45.0 g/L;In the conditions of neutral-weak acid and weak oxidizing environment,the uranium species were dominated by the UO2CO3 and UO2(OH)3-,uranium was deposited or adsorpted,and the uranium concentration was 41.0 ?g/L.EOZ: weak hydrodynamics existed,234U/238U=1.2~1.7,and mainly mixing and evaporation,dominanted by the Cl-Na or Cl-Na.Mg types,TDS>200g/L;with the neutral or alkalinity and strong oxidizing conditions,major uranium species were the UO2(CO3)34-and UO2(CO3)22-,which favored uranium enrichment.The average concentration uranium was up to 146.99?g/L.(5)The evaporation experiment suggested that uranium was concentrated during the evaporation.The salt field evaporation processing showed that the uranium enrichment degree was different,the stage of the sylvinite and carnallite were shown with high effect in that the degree of uranium enrichment up to twofold than the initial intercrystalline brine;and it revealed that uranium was concentrated 40 times higher than in the filtering intercrystalline system.(6)The reasons of the high concentration uranium in the GHSL brine were as follows:(a)long-term water rock interaction of the U-bearing rock provided uranium continuously under the hydraulic migration;(b)the strong-weak hydraulic conditions and oxidization-reduction-oxidization environment benefited uranium migration in this “High Mountain and Deep Basin”;and(c)the evaporation environment facilitated uranium enrichment.