Patent Application: US-84200704-A

Abstract:
a method for passivating sulfidic iron - containing rock comprising : contacting sulfidic iron - containing rock with a magnesium - containing substance , a manganese - containing substance , and a calcium - containing substance ; and adjusting the ph of the system to below about 11 , is provided . the method can be used to prevent acid rock drainage of metal - bearing rocks or to produce a pretreated ore or rock which can be contacted with a lixiviating agent to extract metals from the pretreated ore or rock .

Description:
the ores that may be treated using the method of the invention include pyrrhotite , bornite , chalcopyrite , arsenopyrite and pyrite . any ore that contains iron and sulfur in its reduced form ( sulfide ) may be treated to passivate the sulfur using the disclosed process . the ore may be in any form , for example , slurry , rock pile or exposed rock . the reaction proceeds for a suitable time required to achieve the desired amount of passivation of the ore . this time naturally depends on the nature of the ore treated , the desired amount of passivation of the rock and other parameters , such as concentration of reactants used . this time is readily determined by routine experimentation well within the skill of one of ordinary skill in the art without undue experimentation , using the teachings herein . the processes of this invention can be carried out at temperatures above the freezing point of the solutions up to about 60 ° c . applicant does not wish to be bound by any theory presented herein . the theory and examples below are presented to aid in the understanding of the invention and illustrating some of the presently - preferred embodiments of the invention . experimental materials : the materials used in the study were sulfidic rock , reagent - grade potassium permanganate , reagent - grade manganous sulfate ( mn ( so 4 ) 2 . h 2 o ) and reagent - grade magnesium oxide . calcium oxide and sodium hydroxide were used . sulfidic rock : fresh and weathered sulfidic rock was obtained from the golden sunlight mine located in jefferson county in southwestern montana approximately 55 kilometers east of butte . the golden sunlight mine property is located on the eastern flank of the fault - bounded bull mountain range . during the cretaceous period , proterozoic clastic sedimentary rocks were deposited by latite magmas . the main orebody is the mineral hill orebody and contains gold mineralization that occurs within and around a 200 - meter diameter breccia pipe which cuts sedimentary and igneous rocks . the mineral hill ore body contains gold that occurs primarily as disseminated and structurally - controlled micro - sized particles of free gold and gold tellurides . based on mineralogical studies , precious metal mineralization in the mineral hill porphyry system contains : au , ag , te , bi , cu , fe and ba . weathered material was obtained from a bench high up on the southwestern edge of the pit . the material consisted of blasted waste rock and was probably mined more than 10 years ago . fresh material was obtained from the west side of the pit near the current ore zone ( about 800 feet below the elevation of the location of the weathered rock ). this excavation is done using pre - splitting and fine rock fragments were obtained from the waste rock samples off the bench . general procedure : the general procedure for testing the effectiveness of passivation was : 1 . blank : a sample of the rock was tested without any preparation . this test provides an indication of the acid producing capability of the ore . 2 . control : the ph of a rock sample was adjusted to that required by the procedure ( see discussion below ). 3 . passivation : the ph of a rock sample was adjusted and passivation chemicals were added ( as discussed below ). passivation experiments are designated “ pass ” in the figures herein . this test indicated the success or failure of the passivation procedure . a success of the passivation procedure was found when the ph of the sample was above 7 as long as the test was monitored . 10 - g of ¼ in . passing rock sample 20 - ml di water 1 . 10 - g of ¼ in . passing rock sample 2 . add 20 - ml di water 3 . monitor the ph for three hours 4 . wash and filter the sample 1 . add 85 - ml di water and 15 - ml of 30 % hydrogen peroxide 2 . monitor the ph as a function of time . ( i ) sample preparation procedure : this procedure is modified at times and noted in the following listing . 1 . 10 - g of ¼ in . passing rock sample 2 . add 20 - ml di water 3 . add a predetermined amount of cao to reach a target ph . 4 . add naoh if necessary to reach a target ph and to maintain a target ph . 5 . monitor ph for three hours 6 . wash and filter the sample 1 . add 85 - ml di water and 15 - ml of 30 % hydrogen peroxide solution 2 . monitor ph as a function of time ( i ) sample preparation procedure : this procedure also will be modified at times and will be noted in the recipe table . 1 . 10 - g of ¼ in . passing rock sample 2 . add 20 - ml di water 3 . add a predetermined amount of cao and mgo 4 . adjust ph to 12 with naoh 5 . add 0 . 01 % potassium permanganate ( 0 . 1 - g kmno 4 per 1 - liter di water ) 6 . monitor ph for three hours 7 . filter and wash sample 1 . add 85 - ml di water and 15 - ml of 30 % hydrogen peroxide solution 2 . monitor ph as a function of time ( i ) sample preparation procedure : this procedure also will be modified at times and will be noted in the recipe table . 1 . 10 - g of ¼ in . passing rock sample 2 . add 20 - ml di water 3 . add a predetermined amount of cao and mgo 4 . adjust ph to 12 with naoh 5 . add manganous sulfate . change this as necessary 6 . monitor ph for three hours 7 . filter and wash sample 1 . add 85 - ml di water and 15 - ml of 30 % hydrogen peroxide solution 2 . monitor ph as a function of time fresh rock : 10 - g of ¼ in . passing rock sample ( the rock passes through a ¼ inch opening ). weathered rock : the weathered rock sample of ¼ in . passing material was placed in a no . 40 usa standard testing sieve . the ore was then vigorously washed with tap water with a hose in the lab sink for several minutes . this removes much of the weathering products from the weathered sample . the experimental results are divided into two sections denoted by manganese additions , i . e ., potassium permanganate and manganese salts . in each section the results are shown in graphical form . a table precedes each graph to provide information on experimental conditions . the tables are organized as follows : chemicals used . the chemicals used are described above . in the case of permanganate sufficient amounts were added to maintain a magenta color . in some cases , e . g . table 4 , the differences in the amount of permanganate is due to maintaining a magenta color during the test . ph data . the ph data refers to the initial and final ph during the passivation step . variation occurred during this time period as the acidity of the sample increased and the ph was adjusted with sodium hydroxide . run time . this is the time period for the passivation step of the test and always consisted of 180 minutes contact time of the rock sample and the passivation chemicals . it is known in the art this parameter can be altered as desired to achieve the desired passivation level . 2 . the remainder columns information to identify the variable that is changed in the passivation tests . weathered rock samples were used for the potassium permanganate testing and fresh rock samples were used for the manganous salt testing . in the description provided , an amount of substance per ton indicates per ton of solution . for example , in table 1 , the description “ cao kg / ton ” indicates the listed amount of cao per ton of solution was used . in addition , the description “ kg / ton mgo ” indicates the listed amount of mgo per ton solution , for example . the first series of experiments involved studying the effect of mgo addition while maintaining the other parameters constant . the addition of cao was 0 . 52 kg cao / ton solution and 0 . 05 kg kmno 4 / ton solution . initial ph was 11 . 5 . as shown in fig1 , passivation is achieved with the addition of 0 . 15 kg mgo / ton solution and 0 . 23 kg mgo / ton solution . the results of the blank and control tests are also shown to demonstrate that the rock sample generates acid . these experiments were repeated using less permanganate ( 0 . 04 kg / ton instead of 0 . 05 kg / ton ) and the results can be seen in fig2 . very good reproducibility was obtained at the lower permanganate dosage . experiments were then conducted with lower and higher additions of mgo and at different concentrations of permanganate . these results are given in fig3 . as can be noted , the ph decreased after about 120 minutes when 0 . 08 kg mgo / ton solution was added even at much higher permanganate dosage . passivation is obtained with 0 . 33 kg mgo / ton and 0 . 61 kg mgo / ton solution . in the absence of kmno 4 and cao , passivation is not achieved with 0 . 30 kg mgo / ton solution , 0 . 45 kg mgo / ton solution , and 0 . 57 kg mgo / ton solution ( see fig5 ). the addition of lime with these same levels of mgo did not result in passivation in the absence of permanganate ( fig6 ). passivation fails quickly for the weathered rock from the golden sunlight mine in the absence of kmno 4 with mgo additions of 1 . 93 kg / ton and 3 . 78 kg / ton , even in the presence of cao when the ph is below 12 ( fig8 ). an experiment was conducted to establish the composition of the precipitate that is formed when potassium permanganate , magnesium oxide , and calcium oxide are combined at high ph . in this case 2 . 08 kg cao / ton solution , 0 . 09 kg mgo / ton solution , 20 - ml di water , and 0 . 08 kg kmno 4 / ton solution were combined at ph 12 in the absence of rock sample . the mixture was conditioned for three hours , and the precipitate was separated from solution using an ultracentrifuge . the solid was air - dried , and an x - ray diffraction pattern was obtained . this pattern is given in fig9 . the solids present under these conditions are : mgo 0 . 90 mno 0 . 10 , mgo and periclase , mgo . since the solid noted in the permanganate series of experiments was a manganous compound , experiments were run to determine whether manganous salt additions would result in passivation . manganous nitrate and sulfate were both investigated . the initial experiments were conducted with relatively - high additions of both salts . the composition of the manganous salt did not make a difference ( fig1 ). manganous sulfate was selected for use in subsequent tests . the effect of the amount of manganous sulfate addition was examined . manganese additions of 1 . 46 , 1 . 19 , 0 . 93 and 0 . 56 kg / ton were made with constant additions of cao and mgo . passivation occurred when 1 . 46 and 1 . 19 kg / ton of manganous sulfate was used ( fig1 ). as shown in fig1 , when 0 . 31 kg mgo / ton solution and 1 . 19 kg manganous sulfate / ton solution are present , passivation was not achieved in the absence of cao . passivation was achieved in the presence of 0 . 08 kg / ton and 0 . 13 kg / ton cao , however . an experiment was conducted to establish the composition of the precipitate that is formed when manganous sulfate , magnesium oxide , and calcium oxide are combined at ph 10 . 5 . in this case a solution of 1 . 19 kg mn ( so 4 ) 2 . h 2 o / ton solution , 0 . 39 kg cao / ton solution , 0 . 31 kg mgo / ton solution , and 20 - ml di water was prepared in the absence of a rock sample . the mixture was conditioned for three hours , and the precipitate was separated from solution using an ultracentrifuge . the solid was air dried . the air dried solid contained a light colored powder and a dark colored powder . an x - ray diffraction pattern was obtained for each powder . the database for the light colored powder is shown in fig1 , and the x - ray diffraction pattern for the light colored power is shown in fig1 . the x - ray pattern ( fig1 ) indicates the presence of the following solids : the database for the dark colored powder is shown in fig1 , and the x - ray diffraction pattern for this power is shown in fig1 . the x - ray pattern indicates the presence of the following solids : a passivation solution was prepared under the conditions shown in table 15 . the eh of the solution was measured to be 70 mv . a 30 - g sample of golden sunlight fresh rock ( ¼ in . passing ) was added to the solution , and the eh was monitored for three hours . see fig2 . in the case of weathered rock , sample preparation involved screening and washing the sample to remove the weathering products ( soluble products and very small particles ) from the surface of the rock . this was done because the ph did not lower when testing the control sample with hydrogen peroxide in the control experiment . fresh rock did not pose such a problem and was used as is . caruccio , f . t ., geidel , g ., pelletier , m ., “ occurrence and predication of acid drainage ”. j . of the energy division , asce , 107 , no . 1 , pp . 167 , 1981 . de vries , nadine h . c . process for treating iron - 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( eds . ), society of mining engineering . 1990 . evangelou , v . p ., “ pyrite chemistry : the key for abatement of acid mine drainage ”. acidic mining lakes : acid mine drainage , limnology and reclamation springer - verlag , 1998 . huang , x . and evangelou , v . p ., abatement of acid mine drainage by encapsulation of acid producing geological materials , us bureau of mines , contract no . j0309013 , 1992 . kleinmann , r . l . p ., “ acid mine drainage : us bureau of mines researches and develops control methods for both coal and metal mines ”. enviro . mining j ., july , pp 161 - 164 , 1989 . marshall , g . p ., j . s . thompson , and r . e . jenkins , “ new technology for the prevention of acid rock drainage ”. proceedings of the randol gold and silver forum , pp . 203 - 206 , 1998 . sobek , a . a ., schuller , w . a ., freeman , j . r ., and smith , r . m ., field and laboratory methods applicable to overburden mine soils . epa 600 / 2 - 78 - 054 , pp 203 , 1978 . arnold , d . e ., 1991 , diversion wells — a low - cost approach to treatment of acid mine drainage , in : proceedings of the 12 th annual west virginia surface mine drainage task force symposium , morgantown , w . va ., april 3 - 4 . chen , songyuan , 2001 , control of acid mine drainage by passivation of reactive acid generating materials , a dissertation for the degree of doctor of philosophy in metallurgical engineering , university of nevada , reno , 107 pp . evangelou , v . p . 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( bill ), seta , ananto k ., 1998 , “ acid mine drainage ” encyclopedia of environmental analysis and remediation , john wiley and sons , inc ., pp 1 - 17 . lewis , c . j ., and boynton , r . s ., 1995 , acid neutralization with lime for environmental control and manufacturing processes : arlington , va ., national lime association , 16 pp . mehta , r ., chen , s ., misra , m ., 2000 , “ development of a process to prevent acid generation from waste rock and mine tailings ”, “ environmental issues and management of waste and mineral production ”, r . k . singhal and a . k . mehrota ( eds .) balkema , pp . 577 - 580 . paredes , maria m ., ( 1994 ) a fluid inclusion isotope and multi - element study of the golden sunlight deposit , montana , a thesis for the degree of master of science , iowa state university . parisi , d ., horneman , j . and v . rastogi , 1994 , use of bactericides to control acid mine drainage from surface operations . in : proceedings of the 3 rd international conference on the abatement of acidic drainage , volume 1 . pittsburgh , pa ., pp . 319 - 325 parker , g . and robertson , a ., 1999 , acid drainage . australian minerals and energy environment foundation occasional paper number 11 , australian minerals and energy environment foundation , melbourne , 227 pp . rastogi , v ., 1996 , water quality and reclamation management in mining using bactericides . mining engineering , 48 : pp . 71 - 76 . sengupta , m ., 1993 , environmental impacts of mining : monitoring , restoration , and control . lewis publishers , new york , 494 pp . singer , p . c . and stumm , w ., 1970 , acidic mine drainage : the rate - determining step , science , 167 , p . 1121 . skousen , j ., rose , a ., geidel , g ., foreman , j ., evans , r ., hellier , w ., 1998 , handbook of technologies for avoidance and remediation of acid mine drainage , the national mine land reclamation center , morgantown , w . va ., 131 pp . skousen , j . g and ziemkiewicz , p . f ., 1996 , acid drainage : control and treatment : morgantown , w . va ., west virginia university and the national mine land reclamation center , 361 pp . stumm , w . and morgan , j . j ., 1970 , aquatic chemistry , john wiley and sons , new york . thompson , jeffery s ., marshall , gary p ., 1998 , dupont passivation technology chemistry and application , internal dupont publication . all numerical ranges given herein include all useful intermediate ranges and individual values thereof . useful ranges and values may be determined using the teachings herein and those known in the art without undue experimentation . useful chemical equivalents may be used for those chemicals specifically exemplified in this disclosure , as known by one of ordinary skill in the art without undue experimentation . all references cited herein are hereby incorporated by reference to the extent not inconsistent with the disclosure herein . although the description herein contains many specificities , these are not to be construed as limiting the scope of the invention , but as merely providing illustrations of some of the presently - preferred embodiments of the invention . for example , magnesium may be in the form of magnesium oxide , or other forms , as known in the art . the magnesium -, manganese - and calcium - containing substances may be different chemical species than described herein , as known in the art . in addition , the reaction time may be different than specifically shown . thus , the scope of the invention should be determined by the appended claims and their legal equivalents , rather than by the examples given .