Methods from removing heavy metals from water using chemical precipitation and field separation methods

Abstract

A two-step chemical precipitation process involving hydroxide precipitation and sulfide precipitation combined with “field separation” technology such as magnetic separation, dissolved air flotation, vortex separation, or expanded plastics flotation, effectively removes chelated and non-chelated heavy metal precipitates and other fine particles from water. In the first-step, the non-chelated heavy metals are precipitated as hydroxides and removed from the water by a conventional liquid/solids separator such as an inclined plate clarifier to remove a large percentage of the dissolved heavy metals. The cleaned water is then treated in a second precipitation step to remove the residual heavy metals to meet discharge limits. In the second precipitation step, any metal precipitant more effective than hydroxide for metal precipitation can be used. The invention improves metal removal, lowers cost because fewer chemicals are used, produces less sludge, and reduces the discharge of toxic metals and metal precipitants to the environment. Magnetic separation is preferred for the separation of particles precipitated in the second stage. Similar methods can be employed for separation of other particulates from water. Particulates can also be removed by causing them to adhere to particles of expanded plastic, forming a floc lighter than water, so that the floc can be removed by flotation.

1 - 30 . (canceled) 
     
     
         31 . A method of treating water, comprising the steps of:
 a. directing the water to be treated into a flocculation zone;   b. mixing magnetic seed and a flocculant with the water and causing particulate matter in the water to attach to the magnetic seed to form a magnetic floc that can be attracted by a magnetized surface;   c. mixing the magnetic floc and water in the flocculation zone and maintaining at least some of the magnetic floc in suspension in the flocculation zone;   d. driving a first rotary magnetic separator in the flocculation zone such that at least a portion of the first rotary magnetic separator is submerged in the water in the flocculation zone;   e. collecting magnetic floc from the water in the flocculation zone on the first rotary magnetic separator;   f. removing the magnetic floc from the first rotary magnetic separator; and   g. separating the magnetic seed from the magnetic floc removed from the first rotary magnetic separator and recycling the separated magnetic seed.   
     
     
         32 . The method of  claim 31  wherein the first rotary magnetic separator is positioned adjacent an upper surface of the water in the flocculation zone. 
     
     
         33 . The method of  claim 31  wherein said step of recycling the magnetic seed includes the steps of returning the magnetic seed to the flocculation zone and mixing the returned magnetic seed with the water in the flocculation zone. 
     
     
         34 . The method of  claim 31  including the further steps of directing the magnetic floc removed from the first rotary magnetic separator to a shear tank, shearing the magnetic floc, and detaching the magnetic seed from the magnetic floc to form sludge. 
     
     
         35 . The method of  claim 34  including the further steps of driving a second rotary magnetic separator, collecting the detached magnetic seed on the second rotary magnetic separator, removing the magnetic seed from the second rotary magnetic separator, and recycling the magnetic seed. 
     
     
         36 . The method of  claim 35  wherein the second rotary magnetic separator is disposed adjacent a sludge collection surface and the method includes the step of collecting the sludge on the sludge collection surface. 
     
     
         37 . The method of  claim 35  including the further steps of scraping the magnetic seed from the second rotary magnetic separator and directing the magnetic seed scraped from the second rotary magnetic separator to the flocculation zone. 
     
     
         38 . The method of  claim 35  including the further step of driving the first and second rotary magnetic separators with a common drive source. 
     
     
         39 . The method of  claim 31  including the further steps of driving a second rotary magnetic separator and collecting the magnetic seed separated from the magnetic floc on the second rotary magnetic separator. 
     
     
         40 . The method of  claim 39  including the further step of shearing the magnetic floc to separate the magnetic seed from the magnetic floc prior to collecting the magnetic seed on the second rotary magnetic separator. 
     
     
         41 . The method of  claim 40  including the further step of shearing the magnetic floc in a shear chamber that is separated from the flocculation zone. 
     
     
         42 . The method of  claim 39  including the further steps of disposing at least a portion of the second rotary magnetic separator over the flocculation zone, and removing the collected magnetic seed from the second rotary magnetic separator such that as the magnetic seed is removed from the second rotary magnetic separator, the magnetic seed falls into the flocculation zone. 
     
     
         43 . The method of  claim 31  wherein the magnetic seed is magnetite and the method includes the step of mixing magnetite with the water. 
     
     
         44 . The method of  claim 31  wherein the flocculation zone is disposed in a single tank and wherein substantially all of the particulate matter removed from the water is removed while the water is confined within the single tank. 
     
     
         45 . The method of  claim 35  wherein the flocculation zone is disposed in a single tank and the method includes the steps of directing the water to be treated into the single tank, removing substantial particulate matter from the water while the water is confined within the single tank, and directing a clean and treated water effluent from the single tank. 
     
     
         46 . The method of  claim 45  wherein a third rotary magnetic separator is positioned adjacent an outlet of said tank and the method includes the further steps of directing the water towards the outlet, driving the third rotary magnetic separator and collecting magnetic floc from the water on the third rotary magnetic separator prior to the water being discharged from the outlet. 
     
     
         47 . The method of  claim 46  including driving the first, second and third rotary magnetic separators with a common drive source. 
     
     
         48 . A water treatment system for removing particulate matter from water, comprising:
 a. a single tank having an inlet through which water to be treated enters the tank and an outlet through which treated water is discharged from the tank;   b. one or more injection sites for injecting magnetic seed and a flocculant into the water;   c. a mixer disposed in the single tank for mixing the magnetic seed and flocculant with the water to form magnetic floc, and for maintaining at least a portion of the magnetic floc in an upper portion of the water contained within the tank;   d. a first rotary magnetic separator disposed in an upper portion of the single tank such that when water to be treated is contained within the tank, the first rotary magnetic separator is at least partially submerged in the water;   e. a drive for driving the first rotary magnetic separator such that as the first rotary magnetic separator rotates through the water in the tank, magnetic floc from the water is collected on the first rotary magnetic separator; and   f. whereby particulate matter in the water is removed therefrom while the water is confined within the single tank.   
     
     
         49 . The system of  claim 48  including a removing device for removing magnetic floc from the first rotary magnetic separator, and a shearing device for shearing the removed magnetic floc to yield magnetic seed and sludge. 
     
     
         50 . The system of  claim 49  wherein the shearing device includes a shear chamber, and wherein the system is configured to direct magnetic floc removed from the first magnetic separator to the shear chamber. 
     
     
         51 . The system of  claim 49  including a second rotary magnetic separator for collecting magnetic seed after the magnetic seed has been separated from the magnetic floc, and wherein the collected magnetic seed can be recycled to the single tank. 
     
     
         52 . The system of  claim 51  further including a sludge collection surface disposed adjacent the second rotary magnetic separator for receiving the sludge. 
     
     
         53 . The system of  claim 51  wherein the second rotary magnetic separator is disposed at least partially over the single tank and disposed at least partially above the upper surface of the water. 
     
     
         54 . The system of  claim 48  further including:
 a. a shear chamber for shearing magnetic floc and yielding magnetic seed and sludge;   b. a first device for removing collected magnetic floc from the first rotary magnetic separator;   C. a transfer device for transferring removed magnetic floc to the shear chamber;   d. a second rotary magnetic separator for collecting magnetic seed produced by the shearing chamber; and   e. a second removing device for removing the magnetic seed from the second rotary magnetic separator.   
     
     
         55 . The system of  claim 54  wherein the second removal device is configured to direct the magnetic seed into the single tank. 
     
     
         56 . The system of  claim 54  including a sludge collection surface disposed adjacent the second rotary magnetic separator for collecting sludge. 
     
     
         57 . A method of employing magnetic seeding and a magnetic separator to treat and clarify water in a single tank, comprising the steps of:
 a. directing water having particulate matter therein into the single tank;   b. injecting magnetic seed and a flocculant into the water;   c. forming magnetic floc in the tank by binding particulate matter to the magnetic seed, such that the magnetic floc can be attracted by a magnetic surface;   d. agitating the magnetic floc in the tank to maintain a substantial portion of the magnetic floc in suspension and in an upper portion of the water within the tank;   e. driving a first rotary magnetic separator positioned in an upper portion of the tank, and moving at least a portion of the first rotary magnetic separator through an upper portion of the water in the tank;   f. removing particulate matter from the water in the tank by magnetically collecting the magnetic floc on the first rotary magnetic separator as the first rotary magnetic separator rotates through the water;   g. discharging clarified water from the tank; and   h. wherein substantially all of the particulate matter removed from the water is removed while the water is confined within the single tank.   
     
     
         58 . The method of  claim 57  including the further steps of separating the magnetic seed from the magnetic floc and recycling a portion of the separated magnetic seed to the single tank. 
     
     
         59 . The method of  claim 58  wherein said step of separating the magnetic seed from the magnetic floc includes the steps of shearing the magnetic floc and forming a mixture of sludge and magnetic seed, directing the mixture to a second rotary magnetic separator, collecting the magnetic seed on the second rotary magnetic separator, scraping the magnetic seed from the second rotary magnetic separator, transferring the magnetic seed to the single tank, and collecting the sludge on a sludge collecting surface. 
     
     
         60 . The method of  claim 59  comprising the step of driving the first and second rotary magnetic separators with a common drive source.