the polyvalent metal chelates used herein are aqueous soluble , polyvalent metal chelates of a reducible polyvalent metal , i . e ., a polyvalent metal which is capable of being reduced and a chelating or complexing agent capable of holding the metal in solution . as used herein , the term polyvalent metal includes those reducible metals having a valence of two or more . representative of such polyvalent metals are chromium , cobalt , copper , iron , lead , manganese , mercury , molybdenum , nickel , palladium , platinum , tin , titanium , tungsten and vanadium . of said polyvalent metals , iron , copper and nickel are most advantageously employed in preparing the polyvalent metal chelate ; with iron being most preferred . the term &# 34 ; chelating agent &# 34 ; is well - known in the art and references are made thereto for the purposes of this invention . chelating agents useful in preparing the polyvalent metal chelate of the present invention include those chelating or complexing agents which form a water - soluble chelate with one or more of the aforedescribed polyvalent metals . representative of such chelating agents are the aminopolycarboxylic acids , including the salts thereof , nitrilotriacetic acid , n - hydroxyethyl aminodiacetic acid and the polyaminocarboxylic acids including ethylenediaminetetraacetic acid , n - hydroxyethylethylenediaminetriacetic acid , diethylenetriaminepentaacetic acid , cyclohexene diamine tetraacetic acid , triethylene tetraamine hexaacetic acid and the like ; aminophosphonate acids such as ethylene diamine tetra ( methylene phosphonic acid ), aminotri ( methylene phosphonic acid ), diethylenetriamine penta ( methylene phosphonic acid ); phosphonate acids such as 1 - hydroxy ethylidene - 1 , 1 - diphosphonic acid , 2 - phosphono acetic acid , 2 - phosphono propionic acid , and 1 - phosphono ethane 1 , 2 - dicarboxylic acid ; polyhydroxy chelating agents such as monosaccharides and sugars ( e . g ., disaccharides such as sucrose , lactose and maltose ), sugar acids ( e . g ., gluconic or glucoheptanoic acid ); other polyhydric alcohols such as sorbitol and manitol ; and the like . of such chelating agents , the polyaminocarboxylic acids , particularly ethylenediaminetetraacetic and n - hydroxyethylethylenediaminetriacetic acids , are most advantageously employed in preparing the polyvalent metal chelate used herein . most preferably , the polyvalent metal chelate is the chelate of a ferric iron with a polyaminocarboxylic acid , with the most preferred polyaminocarboxylic acids being selected on the basis of the process conditions to be employed . ethylenediaminetetraacetic acid and n - hydroxyethylethylenediaminetriacetic acid are generally particularly preferred . the oxidizing agent used herein to oxidize elemental sulfur to soluble sulfur compounds is preferably sulfur dioxide which can be generated by oxidizing a side stream of hydrogen sulfide . other oxidizing agents that can be used are the alkali metal salts of inorganic oxidizing acids such as perchloric , chloric , hypochlorous and permanganic acids . for the purpose of this invention , an effective amount of a polyvalent metal chelate is that amount ranging from about a stoichiometric amount based on the hydrogen sulfide absorbed to the amount represented by the solubility limit of the metal chelate in the solution . in like manner , an effective amount of an oxidizing agent is that amount ranging from about a stoichiometric amount based on the free sulfur formed to about five times the stoichiometric amount . the temperature in the aforementioned reaction zones should be maintained in the range from 0 ° to 95 ° c . detailed examples of the invention are given below for purposes of further illustrating the invention . a reaction was carried out in a 1 - liter , temperature controlled reactor equipped with a condenser , thermometer , sampling port and fitted spargers for hydrogen sulfide ( h 2 s ), sulfur dioxide ( so 2 ) and air addition . the reactor was charged with 800 gm water and 23 . 7 gms . ( 0 . 0716 moles ) fe + 3 hedta . the temperature was controlled at 60 ° c . and ph was controlled with caustic at 8 . 0 ph during the run . h 2 s was fed to the reactor at a rate of 13 cc / min . for about 9 minutes to give 0 . 005 moles of h 2 s . substantially all of the h 2 s was oxidized , by the ferric iron , to elemental sulfur and the ferric iron was reduced to the ferrous state . the ferrous iron was then regenerated to ferric iron by sparging air to the reactor . air was sparged at a rate of about 700 cc / min . for about 9 minutes . the reaction was then repeated by alternately sparging h 2 s and air for a total of five cycles . the solution was then weighed and filtered onto a tared filter paper for gravimetric determination of sulfur solids and the filtrate was analysed for soluble sodium thiosulfate . analyses showed 1570 ppm sulfur solids and sodium thiosulfate was below the detectable limit (& lt ; 20 ppm ). the reaction was again carried out using the method and conditions of control i , except that sulfur dioxide ( so 2 ) was sparged into the reactor to react with sulfur to form soluble sulfur compounds . so 2 was sparged during each of the five cycles at a rate of about 85 cc / min . for 4 minutes or a total of 0 . 0694 mole so 2 . analyses showed only 36 ppm sulfur solids and 4562 ppm sodium thiosulfate . to a 1 - liter agitated reactor in a constant temperature bath was added about 500 gm . water , 14 . 8 gm . ( 0 . 0448 mole ) ferric iron - n ( hydroxyethyl )- ethylene diaminetriacetic acid chelate ( fe + 2 . hedta ), and 1 . 15 gm . ( 0 . 0148 mole ) of sodium sulfide as a simulant for the absorption of 0 . 0148 mole of h 2 s . the ph was adjusted to 7 . 0 with nh 4 oh or hcl . the reaction was carried out for 30 minutes at 20 ° c . during which time substantially all of the sulfide was oxidized by the ferric iron to elemental sulfur . the iron was reduced to the ferrous state . the total reaction solution was then weighed and filtered onto a tared filter paper for gravimetric determination of weight percent sulfur solids . the tared filter paper was dried and weighed . the weight percent sulfur solids , based on solution weights , was calculated . the filtrate was analysed for weight percent thiosulfate ( s 2 o 3 = ) and sulfate ( so 4 = ) by ion chromatography . analytical results showed 966 ppm sulfur solids and 164 ppm sodium thiosulfate ( na 2 s 2 o 3 ). sulfate ( so 4 = ) was below detectable limits , i . e ., less than 10 ppm . the reaction was carried out using the method and conditions of control 2 , except that 2 . 95 gms . of sodium sulfite was added . this represents a stoichiometric amount with 50 % excess with respect to the sodium sulfide of control 2 . analytical results showed 149 ppm sulfur solids and 3440 ppm sodium thiosulfate . the reaction was carried out using the method and conditions of control 2 , except the ph was controlled at 8 . 0 . with no sulfite addition ( control 3 ) analysis showed 953 ppm sulfur solids and 232 ppm sodium thiosulfate . with sulfite addition , ( example iii ) analysis showed only 53 ppm sulfur solids and 3412 ppm sodium thiosulfate . the reaction was again carried out using the method and conditions of control 2 except the ph was controlled at 6 . 0 . with no sulfite addition , ( control 4 ) analysis showed 968 ppm sulfur solids and 149 ppm sodium thiosulfate . with sulfite addition , ( example iv ) analysis showed 163 ppm sulfur solids and 3370 ppm sodium thiosulfate . the reaction was again carried out using the method and conditions of control 1 , except that ph was not controlled . the ph fell to about 3 . 6 resulting in nearly complete loss of h 2 s abatement efficiency and loss of so 2 absorption . most of the na 2 s 2 o 3 was probably formed initially at the higher ph . results of the examples and controls are shown in table i . table i______________________________________ ppm ppmph solids na . sub . 2 s . sub . 2 o . sub . 3 remarks______________________________________control 1 8 . 0 1570 n . d . ph control / no so . sub . 2 feedexample 8 . 0 36 4562 ph control / with so . sub . 2 feedcontrol 2 7 . 0 966 164 no sulfite additionexample 7 . 0 149 3440 with sulfite additioniicontrol 3 8 . 0 953 232 no sulfite additionexample 8 . 0 53 3412 with sulfite additioniiicontrol 4 6 . 0 968 149 no sulfite additionexample 6 . 0 163 3370 with sulfite additionivcontrol 5 3 . 6 - 58 2054 no ph contr / with so . sub . 2 feed 8 . 0______________________________________ n . d . -- none detected