Cooperative Agreement S24AC00043

THE PURPOSE OF THIS PROJECT IS TO CORROBORATE RARE EARTH ELEMENT (REE) PREDICTIONS OF THE PHREEQ-NAMDTREAT REYS MODEL (CRAVOTTA, 2022A, 2022B), DEVELOPED WITH PRIOR SUPPORT FROM OSMRE USING THE ESTABLISHEDPHREEQC AQUEOUS GEOCHEMICAL CODE (PARKHURST AND APPELO, 2013). THE PROJECT WILL ACQUIRE NEW EMPIRICAL INFORMATIONTO IMPROVE MODEL PREDICTIONS AND DEMONSTRATE THE MODEL APPLICATION FOR DESIGN OF ACID MINE DRAINAGE (AMD)TREATMENT SYSTEMS FOR OPTIMUM REE RECOVERY THROUGH CAREFULLY CONTROLLED BENCH-SCALE LABORATORY STUDIES. GOALS ARETO (1) DEVELOP A NOVEL TREATMENT PROCESS FOR EFFICIENT RECOVERY OF REES FROM AMD AS HIGH PURITY REE-PHOSPHATECOMPOUNDS (2) EVALUATE THE POTENTIAL FOR RECOVERY OF EXCESS PHOSPHATE FROM MUNICIPAL WASTEWATER TREATMENT PLANTEFFLUENT THROUGH AQUEOUS REACTION WITH AMD METALS AND (3) CONDUCT AN ECONOMIC ANALYSIS OF THE COMBINED COSTS FORTREATMENT AND RESOURCE RECOVERY COMPARED TO REALISTIC VALUE(S) OF THE RECOVERED PRODUCTS, GIVEN ACTUALCOMPOSITION, PURITY, AND QUANTITIES BASED ON EMPIRICAL RESULTS.ONE METHOD FOR OFFSETTING THE COSTS OF AMD TREATMENT IS RECOVERING METALS, LIKE REES, THAT HAVEECONOMICAL VALUE. FOR EXAMPLE, REES CAN BE ELEVATED IN LOW-PH AMD AND IN THE ASSOCIATED TREATMENT SLUDGE(CRAVOTTA, 2008 VASS ET AL., 2019 HEDIN ET AL., 2020). ONE PROMISING OPTION FOR TREATMENT TO RECOVER REE FROMAMD THAT HAS NOT BEEN ADEQUATELY EXPLORED INVOLVES THE ADDITION OF PHOSPHATE (PO4) TO PRODUCE RELATIVELY HIGHPURITY, LOW-SOLUBILITY REEPO4 SOLIDS (LIU AND BYRNE, 1997 MWEWA ET AL., 2022). BECAUSE AL AND FE ALSO FORMINSOLUBLE PO4 COMPOUNDS (OELKERS, AND VALSAMI-JONES, 2008), SEPARATION OF DISSOLVED AL AND FE FROM REE WOULD BENECESSARY TO CONCENTRATE REEPO4. THE PHREEQ-N-AMDTREAT REYS MODEL CAN SIMULATE SUCH A TREATMENT STRATEGYINVOLVING MULTIPLE STEPS THE MODEL INDICATES EFFICIENT RECOVERY OF REEPO4 SOLIDS MAY BE ACHIEVED AT NEAR-NEUTRALPH UPON THE ADDITION OF A SMALL AMOUNT OF DISSOLVED PO4, AFTER INITIAL STEPS TO REMOVE AL AND REDUCE ALL FE TOFE2 . THIS APPROACH COULD BE MORE ECONOMICAL AND HAVE GREATER ENVIRONMENTAL BENEFITS THAN PROCESSING EXISTINGSLUDGE WITH ACID AND SOLVENTS AND ADDING MUCH HIGHER CONCENTRATIONS OF OXALATE TO PRECIPITATE REE FROM ACIDICLEACHATE (E.G. WANG ET AL., 2021).WE PROPOSE TO CONDUCT BENCH-SCALE EXPERIMENTS AT SAINT FRANCIS UNIVERSITY TO VERIFY THE MODELEDPRODUCTION OF REEPO4 SOLIDS AND TO EVALUATE THE POTENTIAL ECONOMICS OF ALTERNATIVE TREATMENT STRATEGIES THATUTILIZE CHEMICAL AGENTS (E.G. NA3PO4) OR NUTRIENT-RICH EFFLUENT FROM MUNICIPAL WASTEWATER TREATMENT PLANTS(WWTPS). THE UNIVERSITY OF RHODE ISLAND WILL ANALYZE THE SOLIDS GENERATED FROM EXPERIMENTS FOR REE CONTENT.ADDING LOW VOLUMES ( 10%) OF WWTP EFFLUENT TO AMD AT AN INTERMEDIATE TREATMENT STEP COULD BE EFFECTIVE FORRECOVERY OF REEPO4. IN SEPARATE STEPS, INTRODUCTION OF METHANE FROM THE WWTP OR CHEMICAL ADDITIONS OF SODIUMMETABISULFITE MAY BE EFFECTIVE FOR REDUCING ALL FE TO FE2 , AND FURTHER ADDITION OF THE WWTP EFFLUENT AT A LATERSTEP COULD RESULT IN THE PRODUCTION OF FE3(PO4)2 (VIVIANITE), WHICH HAS VALUE FOR FERTILIZER AND CAN BEMAGNETICALLY SEPARATED FROM OTHER SOLIDS (PROT ET AL., 2019) (FIGURE 1). APPROXIMATELY, 15% OF THE AMDDISCHARGES, 22% OF THE UNDERGROUND MINES, AND 16% OF THE SURFACE MINES IN PENNSYLVANIA ARE WITHIN TWO MILES OF AWWTP AND 20% OF THE WWTPS SIT ON TOP OF PREVIOUSLY MINED COAL SEAMS (PA DEP, 2020 PASDA, 1996) SIMILARPERCENTAGES ARE EXPECTED FOR OTHER MINING REGIONS IN THE UNITED STATES, ESPECIALLY APPALACHIA. COMPLETING THISPROJECT WILL NOT ONLY INFORM GEOCHEMICAL MODELING BUT WILL RESULT IN CLEAR EXPECTATIONS OF POTENTIAL ADDITIONALBENEFITS FROM RESOURCE RECOVERY ASSOCIATED WITH AMD TREATMENT, COUPLED WITH THOSE FROM WWTPS. THIS WORK COULD BEAPPLIED TO ALL MINING REGIONS WHERE THERE IS POTENTIAL TO RECOVER REES FROM MINE DRAINAGE AND PO4 FROMWASTEWATER.