Abstract: An apparatus and method for removing contaminating metal ions and sulfate ions from acidic aqueous solution such as waste mine water which features passing the solution between pairs of electrodes, each pair of electrodes impressed with a voltage selected according to specific ion species and then adding chemical agents to raise the pH and form precipitates of the metal and sulfate ions. A magnetic field is applied during at least the first mixing step. The precipitate is then separated from the water with settling and filtering steps. The clarified solution is treated by reverse osmosis to concentrate the ammonium.

Abstract: In the method for the humid treatment of effluents containing a compound selected from the group consisting of H.sub.2 SO.sub.4, free SO.sub.2, SO.sub.3.sup.-, or SO.sub.4.sup.= and having a pH lower than 5, the effluents are reacted with a basic compound. Particles selected from the group consisting of CaCO.sub.3.MgCO.sub.3, MgCO.sub.3 and a mixture of these, are used for treating the said effluents, the said particles having a particle size such that at least 95% of the particles selected from the group consisting of CaCO.sub.3.MgCO.sub.3 and MgCO.sub.3 have a particle size smaller than 75 .mu.m. After treatment magnesium sulfate in the form of a solution or brine is recovered.

Abstract: The present invention relates to a process for treating contaminated water to precipitate metals without increasing the total dissolved solids content. In particular, the invention relates to the use of phosphoric acid and calcium hydroxide or calcium oxide to adjust the pH of chromium contaminated groundwater during the treatment process without increasing the total dissolved solids (TDS).

Abstract: Arsenic and TOC are removed from drinking water or wastewaters by use of finely-divided metallic iron in the presence of powdered elemental sulfur or other sulfur compounds such as manganese sulfide, followed by an oxidation step. A premix may be produced for this process, by adding the iron, sulfur and oxidizing agent to water in a predetermined pH range. The iron and sulfur are mixed for a period of time dependent upon the temperature and pH of the water and the presence of complexing or sequestering minerals and organic acids in the water. An oxidizing agent is added to the mixture and agitating is continued. In a preferred embodiment the oxidizing agent is hydrogen peroxide. Water is decanted from the mixture after a sufficient reaction time, to produce a concentrated premix. This premix can be added to water intended for drinking or to industrial effluents containing toxic materials.

Abstract: A method for removing water-soluble macromolecular compounds is characterized by addition of alkali polyphosphates to an aqueous solution containing residual amounts of cationic, anionic, or amphoteric water-soluble macromolecular compounds, formation of insoluble complexes of the alkali polyphosphate and the water-soluble macromolecular complexes, and separation of the resulting complexes from the aqueous solution. This method does not affect the quality or yield of other important components in the aqueous solution.

Abstract: A method and apparatus for treating wastewater effluent from a commercial car wash provides for collecting and holding the effluent in a first tank for equalization and to a pH of about 7.0 to 9.5, and then transferring the equalized wastewater to a second tank for either caustification or acidification to a first predetermined pH of up to 10.0, and preferably 8.2 to 8.6, and most preferably 8.4, and then adding a coagulant, preferably a polyaluminum chloride (PAC) with a basicity of 45 to 50% at 400 to 600 ppm, to a second predetermined pH of 6.2 to 7.0 and preferably 6.6 to 7.0, and most preferably 6.8, to effect coagulation at the second pH to form treated water and a sludge. The treated water is decanted from the sludge and filtered to remove 1 to 50 micron particulates. The filtered water is acidified and then passed through a weak base anion exchange resin to remove MBAS to provide treated water.

Abstract: A method for dehydrating a waste hydrocarbon sludge, includes the steps of: (a) providing a waste hydrocarbon sludge in the form of an emulsion of water and oil having a water content greater than or equal to about 10% vol; (b) providing a solution of a clarifying agent in formation water; (c) mixing the waste hydrocarbon sludge with the solution so as to provide a sludge-water mixture having a ratio of water to hydrocarbon of at least about 1:1; (d) adding a demulsifier to the sludge-water mixture to provide a sludge-water-demulsifier mixture; (e) heating the sludge-water-demulsifier mixture to a sufficient temperature and holding for a time sufficient to provide a hydrocarbon phase having a water content of less than or equal to about 1% vol.

Abstract: In a method of treating an untreated flow of liquid charged with particles and/or colloids, the flow is caused to flow in a coagulation zone that is kept turbulent and in which the flow is mixed with a coagulant. The untreated flow and a granular material which is insoluble in and more dense than the flow are caused to flow in an intermediate zone in which the granular material is maintained in suspension. The flow with substantially all of the added granular material and the colloids or particles aggregated therein is caused to flow in a sedimentation zone in which a clarified effluent is separated from sludge consisting of the granular material and the aggregated particles or colloids. The sedimentation zone has an undivided flow cross section, with no separator plates and the effluent is caused to flow therein at an average settling speed of at least 15 m/h.

Abstract: There is disclosed a process for improving one or more properties of kaolin comprising:(a) providing an aqueous suspension of particulate kaolin clay;(b) introducing into the aqueous suspension a first reagent comprising a source of alkaline earth metal ions and a second reagent comprising a source of carbonate ions to precipitate an alkaline earth metal carbonate in the said aqueous suspension of the said particulate kaolin clay whereby the said particulate kaolin clay present at the start of the process becomes entrained by and bonded to the alkaline earth metal carbonate to form a composite particulate product which may be used in paper making or paper coating or as a filler or extender in compositions for other applications. The alkaline earth metal ions may be calcium ions provided by calcium hydroxide obtained by slaking lime either in the aqueous suspension or separately. The carbonate ions may be provided by carbon dioxide.

Abstract: The present invention provides an efficient and highly effective method of removing dissolved selenium from a variety of refinery process water and wastewater streams. The present invention also provides a new and effective method of oxidizing selenium and organo-selenium compounds to the selenite [+IV] oxidation state in order to be adsorbed by a metal oxide or metal hydroxide precipitate. The invention includes two continuous stirred-tank reactors (CSTR) operated in series. The stream to be treated and one of several iron salts (ferric sulfate, ferric chloride, etc.) are introduced into the first CSTR, forming ferric hydroxide and ferric oxyhydroxide precipitates. The pH of the first CSTR is automatically controlled by adjusting the injection rate of the ferric salt. The effluent stream from the first CSTR is directed into a second CSTR into which potassium permanganate is introduced.

Abstract: Nuisance concentrations of hydrogen sulfide and other malodorous compounds are controlled in liquid and sludge waste systems by adding alkaline iron. The process removes immediate sulfide and suppresses the formation of further nuisance sulfide with a single application. As the sulfide and other malodors are being mitigated in this process, alkalinity is added to the waste as a reaction by-product, which acts to increase the waste pH, decreasing corrosivity and promoting biological treatability and purification of the waste.

Abstract: The present invention concerns the treatment of an aqueous effluent and consists of ridding it of the iron which it contains, notably in the form of a complex. The method according to the invention consists of treating this effluent by successively a silicate, and a magnesium and aluminium hydroxycarbonate, then decanting and filtering. The method according to the invention is particularly useful in the treatment of photographic effluents.

Abstract: A method for recovering and separating precious and non-precious metals from waste streams, which removes, separates, and recovers such metals in a cost effective manner with more than 95% removal from waste streams and with minimal amounts of unprocessed solids and sludge remaining in the environment. Metals such as chromium, manganese, cobalt, nickel, copper, zinc, silver, gold, platinum, vanadium, sodium, potassium, beryllium, magnesium, calcium, barium, lead, aluminum, tin; and the like are removed and recovered from the waste streams with at least 95% removal and other metals and compounds, such as antimony, sulfur, and selenium are removed and recovered from waste streams with at least 50% removal. The method employs a unique complexing agent comprising a carbamate compound and an alkali metal hydroxide which facilitates the formation of the metals into ionic metal particles enabling them to be readily separated, removed and recovered.

Abstract: The invention relates to a method for treating waste water sludge comprising at least one metal originating from a waste water treatment coagulant, and phosphorus and heavy metals in order to recover said at least one metal and phosphorus and to discharge said heavy metals. In this method said waste water sludge is acidified to dissolve metals contained in the sludge thereby yielding an acidified sludge solution containing at least 1% by weight of at least one metal to be recovered. In a first precipitation stage the pH of said acidified sludge solution is raised to precipitate at least one metal to be recovered as a phosphate, and thereafter the phosphate precipitate is separated, thereby leaving a solution comprising heavy metals. In a second precipitation stage the pH of said solution comprising heavy metals is raised and, if necessary, an appropriate chemical is added to precipitate heavy metals, and thereafter the precipitate is discharged.

Abstract: A process is provided for treating a water to reduce its hardness by performing a series of sequential stages including a primary chemical reaction stage, a secondary chemical reaction stage and a scale removal stage. The primary chemical reaction stage includes the steps of adding a first hydroxide ion donor in the form of lime to an initial water having an initial hardness and reacting the first hydroxide ion donor to form a first portion of a scale and an intermediate water having an intermediate hardness substantially less than the initial hardness. The secondary chemical reaction stage includes the steps of adding a second hydroxide ion donor in the form of caustic to the intermediate water and reacting the second hydroxide ion donor to form a second portion of the scale and a product water having a product hardness substantially less than the intermediate hardness.

Abstract: A multi-stage process is provided for treating a water to reduce its hardness. The feed water is initially heated to a thermal reaction temperature in a heating stage. The heated water is then maintained at or near the thermal reaction temperature for a sufficient residence time to thermally react the water, producing a first portion of a scale from the scale-forming ions in the water while discharging dissolved gases from the water. After the thermal reaction stage, one or more chemical additives in the form of a hydroxide ion donor and optionally a bicarbonate ion donor are added to the heated water in a chemical reaction stage. The chemical additive is chemically reacted with the water in the chemical reaction stage, producing a second portion of the scale from the scale-forming ions in the water.

Abstract: A process for the processing of spent photographic baths of black and white processes, namely developing baths with a preponderant content of alkali sulphite, particularly sodium sulphite, and fixing baths with a preponderant content of thiosulphates, particularly ammonium thiosulphate and/or sodium thiosulphate is proposed and is characterized in that following the deposition of the silver contained in the baths, the spent fixing baths are brought to a pH of approximately 0.5 with concentrated HCl and the elementary sulphur resulting from the decomposition of the thiosulphates is separated, whilst the remaining sulphurous acid intermediate solution is mixed with the spent developing baths and adjusted to a pH of approximately 2 and the resulting, SO.sub.2 -supersaturated solution is heated and pure SO.sub.2 is drawn off in a vacuum. Finally, the residual solution is adjusted to a pH of approximately 10 with Ca(OH).sub.2 and the liberated ammonia is drawn off.

Abstract: A process for treating waste water of flue gas desulfurization comprising successively adjusting the pH of the waste water to 5 or less, bringing the waste water into contact with a column packed with fine particles of iron, flocculating the waste water, removing formed flocs from the waste water by solid-liquid separation, and optionally, bringing the remaining waste water into contact with a resin for COD adsorption, successively. Hazardous substances, such as oxidative substances, peroxosulfuric acid, iodic acid, heavy metals such as copper and lead, and non-metallic substances such as selenium compounds and fluorites, can be removed simultaneously and efficiently from the waste water of flue gas desulfurization containing these hazardous substances by using the process which is a simplified waste water disposal system.

Abstract: The present invention provides a process for treating arsenic-containing waste water, comprising adding an oxidizing agent, if necessary, to arsenic-containing waste water to oxidize trivalent arsenic in the waste water into pentavalent arsenic; adding a calcium compound to adjust the pH to 12 or higher; separating it into solid and liquid (first solid/liquid separation); calcining the resulting sludge, while adding a ferric salt to the treated solution to adjust the pH to 6-9 after the solid/liquid separation; and separating it into solid and liquid (second solid/liquid separation). According to the present invention, it is possible to remove arsenic from waste water efficiently to yield treated water satisfying various tolerance limits under various regulations, while the arsenic-containing sludge separated from the waste water can become harmless in subsequent continuous steps.

Abstract: A method for recovery and use of a particulate waste material, i.e. inorganic and/or organic solid fines, present in an aqueous suspension, comprising the steps of:a) treating the aqueous suspension so as to precipitate, in the presence of the solid fines, crystals of an alkaline earth metal carbonate whereby the solid fines become entrained by and bonded to the crystals, thereby forming in the aqueous suspension a mixed aggregated particulate solid comprising the crystals and the fines; andb) recovering the mixed aggregated particulate solid and supplying such solid for use as a filler or pigment in a filler- or pigment-containing composition.

Abstract: A recycling apparatus which preferably treats used antifreeze/coolant in four cycles is disclosed. The recycling apparatus includes a number of tanks for storing the antifreeze/coolant during the various treatment cycles, a number of containers for storing chemical reagents used to chemically treat the antifreeze/coolant and a number of filters used to capture impurities suspended in the treated antifreeze/coolant. During a fill cycle, the used antifreeze/coolant is introduced into a treatment tank and the concentration of the antifreeze/coolant is adjusted, if necessary, to a predefined range. During a mix cycle, the used antifreeze/coolant is mixed with various reagents to adjust the pH value, as well as to coagulate and flocculate the impurities. A reverse mixing and aspiration of the antifreeze/coolant in the tank during the mix cycle ensure that the reagents will mix well and react with the impurities in the used antifreeze/coolant to form a sludge.

Abstract: A method and apparatus for treating wastewater effluent from diversely laundered household wash as in a laundromat provides for collecting and holding the effluent in a first tank for at least an average wash cycle for equalization and to a pH of 8.5 to 11, and then transferring the equalized wastewater to a second tank for acidification to a first predetermined pH of not less than about 6.5 and preferably 6.5 to 6.9, and then adding a coagulant, preferably a PAC with a basicity of 45 to 50%, to effect a second predetermined pH of not less than about 5.0 and preferably 5.2 to 5.4 for coagulation at the second pH to form treated water and a sludge. The treated water is decanted from the sludge and filtered to remove 1 to 50 micron particulates. The filtered water is then passed through a weak base anion exchange resin to remove MBAS to provide treated water.

Abstract: A system and method for disposing of vacuum degasser contaminants which includes adjusting the pH, in a reactor vessel, of a vacuum degasser underflow stream to precipitate lead and zinc into particulate matter. The solids are then concentrated in a thickener to produce an underflow stream that is communicated to a holding vessel to settle. The overflow from the thickener is filtered through a sand filter and discharged to meet applicable NPDES permit limits. Lime is added to the slurry in the holding vessel to further settle the solids, to aid in filtration, and to prevent leaching of lead from the filter cake during TCLP testing. An overlaying supernatant is decanted from the holding vessel and returned to the reactor vessel for further treatment. Limestone is added to the underflow stream. The resulting slurry is dewatered to produce a friable, non-hazardous filtrate cake and a filtrate. The filtrate is directed back to reactor vessel prior to discharge for further treatment.

Abstract: Mineral slurries such as coal refuse are flocculated to separate solids therefrom by adding a blend of high and low molecular weight cationic flocculants followed by a high molecular weight anionic flocculant.

Abstract: A method and apparatus for treatment of contaminated water, containing undesired solid, liquid, and/or gaseous materials includes an electro-floculation means for disassociating ions from the undesired solid material and from the contaminated water, and further includes a separation tower having various deflection means deflecting undesired solid materials downwardly through to the separation tower.

Abstract: There is disclosed a process for separating fine solids from water in the used water recovery system of a sheet forming mill, wherein the used water recovery system includes at least one stage in which an alkaline earth metal carbonate is precipitated in the aqueous suspension constituting the used water whereby the particulate material present in the used water becomes entrained in the alkaline earth metal carbonate precipitate. By the invention it is possible to recover the water and the fine solid materials which pass through the wire mesh belt of a paper or board forming machine, and optionally recycle those recovered materials.

Abstract: An apparatus and method for removing contaminating metal ions and sulfate ions from acidic aqueous solution such as waste mine water which features passing the solution between pairs of electrodes, each pair of electrodes impressed with a voltage selected according to specific ion species and then adding chemical agents to raise the pH and form precipitates of the metal and sulfate ions. The precipitate is then separated from the water with settling and filtering steps. Application of a magnetic field is applied during at least the first mixing step.

Abstract: For the removal of heavy metal contaminants from industrial waste water, a method is proposed for preparing a dense precipitate having superior handling and disposal properties. The method comprises incremental adjustment of the pH to maintain a low saturation ratio and recycling of slurry to provide seed crystals for secondary nucleation.

Abstract: A process for removing lead from drinking water discharged from a drinking water outlet comprising:(a) directing the water through a first matrix comprising a calcium mineral of between 10 and 100 weight percent of a solid calcium phosphate mineral which is slightly soluble in water, the remaining portion being a solid calcium carbonate mineral which is slightly soluble in water, such that there is sufficient contacting between the water and the first matrix to introduce sufficient phosphate ions into the water to form lead precipitate and reduce the lead concentration in the water to below 15 parts per billion,(b) directing the lead depleted water from step (a) through a second matrix, the second matrix comprising a mineral that when in equilibrium with the water reduces the phosphate ion concentration to 60 mg/L or below.

Abstract: A process for treating acid wastewater containing heavy metals has been invented, the process including adding fly ash to the acid wastewater to reduce heavy metals content of the acid wastewater. In one aspect the acid wastewater contains soluble iron and adding fly ash reduces the level of soluble iron. In one aspect the acid wastewater contains sulfate ions and adding fly ash reduces the sulfate ion level. In one aspect solid silicate salts are added to the acid wastewater. Preferably undesirable very hydrous iron hydroxide precipitate is not formed. In certain aspects the pH of the acid wastewater is raised to an environmentally acceptable level. In one aspect the process is a batch process. In another aspect the process is a continuous process.

Abstract: Impure liquid media containing contaminating amounts of metallic impurities, e.g., alkaline earth metals, heavy metals and/or radioactive elements, for example industrial effluents from the nitric acidulation of rare earth concentrates, are purified by separately introducing a source of phosphorus and a source of barium into the impure medium, whereby precipitating a solid residue which comprises a barium phosphate having such contaminating metallic impurities distributed therein, and thence separating the solid residue from the liquid medium thus purified.

Abstract: A method for removing aluminum from blood includes the step of adding to the blood an anticoagulant and a complexing agent for aluminum or one compound effective in both preventing coagulation of blood and capable of complexing aluminum. The complexing agent or compound capable of complexing aluminum is allowed to intermingle with the blood and complex with aluminum present in the blood. The complex of complexing agent and aluminum formed during the intermingle step is then separated using a semi-permeable membrane, and the blood is recovered. The method is particularly useful in treating patient's having aluminum intoxication.

Abstract: A system and method for removing asbestos and other hazardous solids from a slurry collected during removal of coatings from pipelines, equipment and other structures. The slurry is collected in a collection pan that is attached to a shroud of a hydrocleaning machine. Contaminated air and the slurry is transferred to a vacuum hopper. The contaminated air is removed from the vacuum hopper. The contaminated air is filtered to remove solid particles. Solid particles are preferably separated from the slurry by passing the slurry through various stages of filters. Pumps are used to transfer the slurry from the collection pan through the filter stages. A first flocculent is injected into the slurry to coagulate the solid particles into individual masses. A second flocculent can be injected into the slurry in order to coagulate a majority of the remaining solid particles. The coagulated masses of solid particles are removed by passing the slurry through a weir or a screen shaker.

Abstract: A process for reducing the phosphate content in waste water from the preparation of salts of ascorbic acid 2-monophosphate comprisesA. treating the waste water from the crystallization of the metal salts of ascorbic acid 2-monophosphate with an alkali metal or alkaline earth metal hypochlorite, chlorine or H.sub.2 O.sub.2,andB. precipitating, at a pH of 9-12, the inorganic phosphate which has been produced from organically bound phosphorus and/or was present in the waste water, especially as calcium phosphate.

Abstract: An apparatus for waste water treatment, wherein fluorine contained in waste water is treated into a fluoride through a chemical reaction and sludge containing the fluoride is thickened and dehydrated into a sludge cake, has first and second tanks each packed with calcium carbonate mineral. In the first tank, waster water containing fluorine is agitated by air discharged from an air diffuser and caused to react with the calcium carbonate mineral. Through this reaction of the waste water with the calcium carbonate mineral and action of microorganisms on the surface of the calcium carbonate mineral, a pH value and a fluorine concentration of the waste water is adjusted till the pH value and the fluorine concentration fall within their respective predetermined ranges.

Abstract: Arsenic and TOC are removed from drinking water or wastewaters by use of finely-divided metallic iron in the presence of powdered elemental sulfur or other sulfur compounds such as manganese sulfide, followed by an oxidation step. A premix may be produced for this process, by adding the iron, sulfur and oxidizing agent to water in a predetermined pH range. The iron and sulfur are mixed for a period of time dependent upon the temperature and pH of the water and the presence of complexing or sequestering minerals and organic acids in the water. An oxidizing agent is added to the mixture and agitating is continued. In a preferred embodiment the oxidizing agent is hydrogen peroxide. Water is decanted from the mixture after a sufficient reaction time, to produce a concentrated premix. This premix can be added to water intended for drinking or to industrial effluents containing toxic materials.

Abstract: There is disclosed a process for separating fine solids from water in the used water recovery system of a sheet forming mill, wherein the used water recovery system includes at least one stage in which an alkaline earth metal carbonate is precipitated in the aqueous suspension constituting the used water whereby the particulate material present in the used water becomes entrained in the alkaline earth metal carbonate precipitate. By the invention it is possible to recover the water and the fine solid materials which pass through the wire mesh belt of a paper or board forming machine, and optionally recycle those recovered materials.

Abstract: Process for treating aqueous media containing metal ions having valences of +2 and higher and optionally acid comprising:(a) contacting the aqueous media, at a pH of about 1-5, with an effective amount of product recycled from step (b) to dissolve at least some metal carbonates, produce at least some CO.sub.2, convert at least some metal ions having a valence of at least +3 to metal hydroxide precipitates, and neutralize some acid, if present;(b) contacting the product of step (a), at a pH of about 4-8.5, with an effective amount of Na.sub.2 CO.sub.3 to convert at least some metal ions of +2 valence to metal carbonate precipitates and form at least some dissolved sodium salts;(c) recovering, from a portion of the product from step (b) that is not recycled, metal carbonates, metal hydroxides, and sodium salts.

Abstract: Metals contained in various wastewaters are selectively recovered as metal precipitates and/or as spinel ferrite and water suitable for discharge into the environment is obtained. High grade magnetic spinel ferrite is recovered from wastewaters having aluminum and arsenic if present in the wastewater, removed from the wastewater. There are three process stages for the treatment of wastewater. In the first process stage which is optional, at least a portion of at least one non-ferrous or non-ferric metal is precipitated from the wastewater by subjecting the wastewater to an oxidizing agent to increase the oxidation-reduction potential of the water, by adjusting the pH of the wastewater to a pH at which the metal precipitates from the water and by adding an organic or inorganic sulfur compound, capable of causing the metal to form a precipitate, to the water in a quantity sufficient to precipitate the metal.

Abstract: Materials and methods relating to water treatment processes are described. More specifically, the process is non-toxic and is useful for the removal of algae, other suspended solids, or contaminants in surface waters or in potable water treatment. Coccolithic calcium carbonate can be used in combination with a flocculent such as aluminum chloride to obtain the desired results.

Abstract: Disclosed is a method to remove heavy metals from amino-carboxylic acid chelate solutions comprising adding nitrous acid to lower the pH of the aqueous solution sufficient to destroy the chelate bonds and release the metal ions and thereafter adding an appropriate strong base and optionally a sulfide salt to precipitate the liberated heavy metals.

Abstract: The invention relates to a process for the purification of a polluted aqueous effluent to obtain an overall reduction in its chemical oxygen demand. The aqueous effluent is introduced into a reactor. Added to the reactor is a reagent comprising an agent supplying active alumina and lime. The reaction forms mineral sludge and an effluent. The mineral sludge and supernatant effluent are then extracted by decantation or filtration.

Abstract: A process for the treatment of acidic fluoride-containing solutions to neutralize them and to remove fluoride ion in the form of a readily filterable precipitate which comprises mixing the acidic solution with a suspension of an alkaline earth metal oxide or hydroxide, wherein a flocculating agent is incorporated in the acidic solution before mixing thereof with the alkaline earth metal oxide or hydroxide.

Abstract: A process for purifying an acidic technical-grade iron chloride solution formed from cyclone dust from the production of TiO.sub.2 in accordance with the chloride process by adjusting the pH with a first neutralizing agent and thereafter introducing the pH adjusted solution in a controlled manner into a solution containing a second neutralizing agent. In this process undesired ions which are to be separated, such as chromium, vanadium, zirconium and/or niobium, precipitate in the form of efficiently filterable hydroxides which can be separated industrially under economical conditions by filtration. The filter cake is non-hazardous and can safely be disposed of by dumping. Calcium carbonate is the preferred neutralizing agent, and the pH adjustment may also advantageously be effected by using scrap iron or by using iron sinters with reduction of any Fe(III) ions before the second neutralization step.

Abstract: A method for removing dissolved fluoride from waste water involving a multiple stage process which includes a first step of contacting a solution comprising calcium fluoride with a calcium ion source to form a first precipitate and a second step of contacting the first precipitate comprising the calcium ion source with the fluoride-containing waste water solution to form a second precipitate. A first portion of the solution that has been treated directly with the waste water and which contains the second precipitate, is preferably recycled, along with calcium fluoride, to the first step for contact with the calcium ion source. A second portion of the solution treated with the waste water may be transported to a thickener or gravity settling step, and/or to a solids-dewatering step wherein standard filtration equipment may be used to produce a filter cake having a controlled particle size distribution.

Abstract: A highly flexible multi-step treatment technology for chemical fixation and stabilization of leachable chromium, particularly hexavalent chrome, in contaminated soils, solid wastes, concrete, sludge, sand and gravel and waste waters is disclosed. The process comprises reducing hexavalent chromium to chromous (Cr.sup.2+) and chromic (Cr.sup.3+) forms in the presence of water under alkaline conditions and fixing the reduced chromium forms with phosphate.The process reduces Toxicity Characteristic Leaching Procedure chromium levels below the regulatory threshold of 5 mg/l as required by the USEPA.

Abstract: Heavy metal ions react with ferrous dithionite in acidic aqueous solution. They are reduced to metallic particles that are suitable for recycling and reuse when recovered from the acidic water. Chelating agents that are present are deactivated by bonding to the ferrous ions. Ferrous dithionite, (FeS.sub.2 O.sub.4) is either generated in-situ or ferrous ions and dithionite ions can be provided by other methods. An alkali metal hydroxide is utilized to precipitate remaining heavy metal ions including ferrous and ferric ions.

Abstract: A method of treating chemical liquid, and in particular photographic effluent, to render it more environmentally acceptable, by the addition to an alkaline solution of a salt of a Group III or transition metal to complex with and precipitate out a sequestering agent. Preferred salts are the sulphate, halide, oxychloride or nitrate of aluminium.

Abstract: A water-treatment process which simultaneously performs degritting, degreasing, coagulation, flocculation and settling. The steps include breaking down into two elementary steps, at least least one of the degritting and degreasing functions and, simultaneously performing at least one of the following associated steps:coarse degritting and coagulation of untreated water;fine degritting and a first step for coalescence of grease particles, and high-energy flocculation;a second step for coalescence of the grease particles and low-energy flocculation, andseparating the greast particles and commencing a settling operation.

Abstract: A process for treating industrial waste water containing hexavalent chromium (Cr.sup.+6) and other heavy metals is disclosed which comprises reduction of Cr.sup.+6 to trivalent chromium (Cr.sup.+3) and the precipitation thereof with other heavy metals by addition of sulfide ion and ferrous ion to the waste stream at a pH of about 7 to 9 under conditions such that sludge production by the process of the invention is substantially less than that characteristic of prior art processes. Polymers are added to the solution to assist flocculation and clarification of the waste stream. More specifically, the invention comprises adding sulfide ion in a sulfide to hexavalent chromium ratio of about 0.7-2.5:1 and adding ferrous ion in a ferrous to hexavalent chromium ratio of about 0.5-5.0:1. The waste stream pH is preferably maintained in the range of about 7.2 to 7.5.