FORAGER® - Type M Sponge
for the removal of heavy metal and inorganic contaminants

GENERAL PROPERTIES

Type M FORAGER® Sponge is an open-celled cellulose Sponge incorporating an amine-containing polymer having selective affinity for heavy metals in cationic and anionic states in aqueous solution.

The highly porous nature of the Sponge speeds diffusional effects, thereby promoting fast rates of absorption of ions. In its currently available size (˝”cubes), the Sponge can be utilized in columns, fishnet-type enclosures, or rotating drums, and is relatively unaffected by suspended matter. In column operations, flow rates of three bed volumes/minute can be obtained at hydrostatic pressures only two feet above the bed, and without additional pressurization. Sponge-packed columns are therefore suitable for gravity flow applications.

The polymer functions by forming coordination complexes preferentially with ions of transition group heavy metals, namely those metals classified in groups IB through VIIIB of the Periodic Table and generally characterized in having incomplete inner rings of electrons or being otherwise capable of existing in more than one valence state. By comparison, metals such as calcium, magnesium and aluminum, having complete inner rings of electrons and single valence states, show poor affinity for the polymer. The polymer provides ligand sites that surround the metal and form a coordination complex. The order of affinity of the polymer for metals is influenced by solution parameters such as pH, temperature and total ionic content. However, the following affinity sequence of some representative ions can generally be expected:

When employed as a stationary bed in a column through which an aqueous stream flows, absorption bands are produced generally in accordance with the affinity sequence. In certain situations, strongly absorbed species will displace less strongly absorbed species. This characteristic may be employed to separate ions. When utilized in an upward flow fluidized bed, or in rotating drums, simultaneous absorption of a number of ionic species will occur in amounts relative to initial concentration and affinity sequence.

At saturation, the Sponge will contain between about 4% and 10% (dry weight basis) of absorbed ions, depending upon the affinity of the polymer for the ion, and the molecular weight of the ion.

APPLICATIONS

In pollution control applications, the Type-M Forager® Sponge has been found useful in scavenging toxic metals in ppm and ppb concentrations from industrial discharges, municipal sewage process streams, groundwater, storm water, landfill leachate, and acid mine drainage waters. Efficiencies of removal of greater than 90% have been achieved. In such applications, the Sponge is generally loaded into a tubular fishnet enclosure which is confined within a tube, or packed into a catch basin, or suspended tea bag style in a flowing stream. Because ambient water pressure is adequate to cause penetration of the confined bed of Sponge, such installations can be employed in remote or otherwise unattended locations, and can be monitored by radio-transmitting sensors. The fishnet installations can be periodically retrieved and replaced with fresh units. In situ remediation of ground water is achievable by positioning fishnet containers of Sponge vertically at the gate of a barrier wall funnel system (see Figure 1). The remediation of ground water using FORAGER® Sponge is described in EPA Superfund Innovative Technology Evaluation Report EPA/540/R-94/522.

In cyanide leach gold mining operations, the Sponge functions at a faster rate than activated carbon in absorbing Au(CN)2- from alkaline slurries and solutions. Gold and other metals can also be recovered from tailings ponds and detoxification rinse water. An interesting phenomenon in such applications is that, after the Sponge saturates with a base metal such as Cu, it will still absorb gold. This characteristic enables the Sponge to recover gold even when other metals exist in the same solution at vastly greater concentrations.

Waste solutions from electroplating, metal finishing and printed circuit board industries have been treated to recover valuable metals and remove toxic species. The Sponge, deployed in cartridge-type filtration modules, removes traces of silver from photo finishing effluents. Trace metals have also been recovered from brines, geothermal wells, ocean water, and swimming pool water. Pourable sludges such as harbor sediments have been treated by tumbling followed by sieving to recover the Sponge.

NOTE: The removal of species such as mercury and vanadium in the ppb concentration range is now achievable with a newly introduced modification of Type M Sponge, designated Type M-TU.

HANDLING

FORAGER® Sponge is marketed in an amber-colored wet form. Drying is to be avoided because it diminishes the efficiency of the Sponge in subsequent usage. Although the Sponge is generally unaffected by compressive mechanical forces, squeezing or comparable deformational stress should be minimized. The Sponge evidences little mechanical degradation or fine production in the course of moderate mechanical handling. In column operations, forceful backwashing can be utilized to float the Sponge out of the column to a regeneration or disposal operation.
Quantitative evaluations of the effectiveness of the Sponge can be done either by assaying the saturated Sponge, or by analyzing the aqueous system before and after treatment by the Sponge. Prior to laboratory evaluations with small volumes of test solution, as in a stirred beaker or shaken flask, the Sponge should be extensively washed with pure water to remove any residual monomers. In such confined evaluations, at least four hours of contact time should be allowed to be assured of saturation. In column evaluations, flow rates in the range of 0.5 to1. 0 bed volumes/minute (bvm) should be studied initially. It should be noted that the efficiency of metals removal varies inversely with flow rate (See Figure 2)

Increased affinity for anions such as CrO4-2 and SiO4-4 can be achieved by pretreating the Sponge with 2% HCl, followed by rinsing with water. Increased affinity for anions such as PO4-3, Au(CN)2-, SeO4-2, UO4-2 and AsO4-3 can be achieved by presaturating the Sponge with a polyvalent cat ion such as Cu++, Fe+3, Al+3 or Mg++. Increased affinity for Cr+3, Ni+2 and Co+2 can be achieved by pretreatment of the Sponge with ammonium hydroxide.

Inorganic anionic species such as cyanides, arsenates, phosphates, silicates, vanadates, tungstates, and selenites can usually be removed by customized grades of FORAGER® Sponge.

Many absorbed ions can be eluted from the Sponge by techniques typically employed for regenerating ion exchange resins. For example, HCl solutions of up to 5% concentration remove many absorbed cations. A solution comprised of 1% NaOH+0.5% NaCN is generally effective in removing Ag, Au, Pd, Pt, and other metals capable of forming cyanide complexes. Solutions of thiosulfate and other complex-forming anions may also be used for elution. Treatment of the metal-saturated Sponge with a dilute solution of NaBH4 will often produce distinctive color changes, and will modify elution characteristics.

Elevated temperatures of up to 40°C may be employed for the elution step. Following elution and washing, the Sponge is ready for the next absorption cycle. The number of useful cycles that can be expected depends upon the nature of the absorbed ions and elution technique. The deposition within the Sponge of certain intractable species such as phosphates and silicates diminishes its life expectancy.

In certain applications utilizing absorption drums, the saturated Sponge may be disposed of along with the drum. The saturated Sponge may also be incinerated, with careful attention given to the handling of the resultant vapors. In some instances, particularly when the absorbed metals are radioactive, the Sponge is preferably compacted to an extremely small volume to facilitate disposal. Boards suitable for structural use can be produced by impregnating the metal-saturated Sponge with heat-curable phenolic or melamine-type prepolymer solutions, and subjecting uniform layers of the impregnated Sponge to a hot pressing operation.

NON-WARRANTY

All data, statements and recommendations contained in this publication are based upon the best information available and are believed to be reliable. However, all such data, statements and recommendations are given gratis, and Dynaphore, Inc. assumes no obligation or liability, and makes no warranty either express or implied, with regard to the data, statements and recommendations given or the application of the products covered in this publication, or the results obtained; all such data, statements and recommendations being given and accepted at the user’s risk. Nothing printed in this publication is to be construed as permission, or a recommendation to practice any patented invention without a license. Although no adverse physiological effects have been observed in the course of our handling of FORAGER® products, the user assumes all risk of its use and handling. No statement herein contained shall be taken as a recommendation of any action or use without independent investigation and the practice of such safety precautions as may be indicated in the particular circumstances to protect health and property.

PATENTS ISSUED AND PENDING