Formation And Regulation Of Metal Sulfide Minerals In The Treatment Of Acid Mine Wastewater By ABR Sulfate Reduction System

Acidic mine drainage（AMD）is characterized by low p H,high sulfate content,and various toxic heavy metal ions.Untreated AMD can often cause serious environmental pollution and damage.The use of sulfate-reducing bacteria（SRB）to treat AMD has significant advantages,but its engineering application is constrained by factors such as the inability to separate multiple heavy metal precipitates and the difficulty in separating heavy metal precipitates from sludge.In this study,a five-compartment anaerobic baffled reactor（ABR）was used to treat sulfate organic wastewater,and an ABR sulfate reduction system was constructed to precipitate heavy metals in AMD in a graded manner by regulating the ABR sulfate reduction system and forming micron-scale minerals through microbial mineralization.This provides a theoretical basis for the separation and recovery of heavy metals from AMD.The main research contents and results are as follows:（1）Using sulfate organic wastewater to start and operate a five-compartment ABR for384 days,an ABR sulfate reduction system was successfully established.In the ABR sulfate reduction system,the average p H values of compartments 1 to 5 were 5.4,5.7,6.8,6.9,and 7.0,the average concentrations of volatile fatty acids（VFAs）were 20,20,7,5,and 5 mmol/L,the average concentrations of sulfides were 136,129,113,110,and 108mg/L,and the sulfate reduction activity of granular sludge was 0.49,0.21,0.19,0.08,and0.02 mg/（g VSS·h）,respectively.The results of 16S r RNA high-throughput sequencing showed that the dominant bacteria in the front-end compartment are mostly acid producing bacteria and SRB,while the dominant bacteria in the back-end compartment are methane producing archaea（MPA）.And the dominant bacteria in compartment 1 were Clostridium IV,Ethanoligenens,and Desulfovibrio,with relative abundances of 35.7%,21.4%,and9.0%,respectively.The dominant bacteria in compartment 2 were Clostridium IV,Clostridium sensu stricto,and Desulfovibrio,with relative abundances of 27.4%,18.8%,and 13.1%,respectively.Methanothrix was dominant in compartments 3,4,and 5,with relative abundances of 23.5%,29.2%,and 59.7%,respectively.This indicates that a clear metabolic phase-separation,p H gradient,and sulfide accumulation has been formed along the ABR sulfate reduction system,which can be used for the graded precipitation of heavy metals in AMD.（2）In the experiment,the continuation of ABR sulfate-reducing system was using simulated AMD.When the influent concentrations of Fe²⁺,Zn²⁺,and Cd²⁺were 300,30,and 15 mg/L respectively,Zn²⁺and Cd²⁺were almost completely removed in the first compartment,while Fe²⁺was primarily removed in the third and fourth compartments with a removal efficiency of 65%.As a result,the average p H values of the first to fifth compartments decreased to 3.3,4.0,5.5,6.0,and 6.2 respectively.The average concentrations of VFAs were 20,23,19,13,and 11 mmol/L,and the average concentrations of sulfides decreased to 6,69,11,49,and 41 mg/L in the respective compartments.The sulfate-reducing activity of the particle sludge in each compartment also significantly decreased,with values of 0.02,0.02,0.02,0.03,and 0.02 mg/（g VSS·h）,respectively.After 132 days of simulated AMD with water inflow,the dominant bacterial genera in the first compartment evolved into Prevotella,Clostridium IV,and Ethanoligenens,with relative abundances of 18.4%,17.3%,and 10.7%,respectively.The relative abundance of Desulfovibrio decreased to 0.4%.The dominant bacterial genera in the second compartment were Clostridium sensu stricto and Megasphaera,with relative abundances of 31.6%and 10.6%,respectively.The dominant bacterial genera in the third compartment were Methanothrix and Desulfovibrio,with relative abundances of 28.5%and 11.9%,respectively.The dominant bacterial genus in the fourth compartment was Methanothrix,with a relative abundance of 69.2%.The dominant bacterial genera in the fifth compartment were Clostridium sensu stricto and Methanothrix,with relative abundances of 19.1%and 19.0%,respectively.After 132 days of simulated AMD with water inflow,the results of SEM-EDS analysis and XRD testing showed that mineral particles with a diameter of 1μm to 5μm were formed on the surface of the particle sludge in the first,second,and third compartments,while mineral particles with a diameter of 0.2μm to 0.5μm were formed on the surface of the particle sludge in the fourth and fifth compartments.The particle sludge in the first compartment contained mainly sulfide minerals such as sphalerite,wurtzite,and cadmium sulfide.The particle sludge in the second to fifth compartments contained mainly sulfide minerals such as pyrite,pyrrhotite,and chalcopyrite.