Organoclays for Water and Waste Treatment

or gan o clay: organically modified clay consisting of bentonite, composed mainly of the clay mineral montmorillonite, which is modified with quaternary amines.

qua ter nar y: consisting of or especially arranged in sets of four.

Organoclays are a class of surface-modified clay compounds that is used for two purposes:

• To absorb and stabilize hazardous organic liquid wastes
• To remove organic compounds from water flows

Given the wide variety of molecular weights, viscosities and Kb-Values found among organic liquids and oils, there is no “One Size Fits All” product that performs ideally along the entire spectrum of possibilities.  That is why the surface treatment is frequently tailored to address the technical needs of the situation at hand.

History and Information on Organoclays for Water Treatment

A wealth of information has been discovered since 1949, when Jordon first published “Organophilic Bentonites. I. Swelling Organic Liquids”, which promoted the idea of the potential use of this family of materials for treating contaminated groundwater and wastewater.

In 1985, Wolfe's paper “Interaction of Aliphatic Amines with Montmorillonite to Enhance Adsorption of Organic Pollutants,” noted in their introduction that "Although organoclays have been recognized as adsorbents of such organic compounds, few studies have been conducted to determine whether certain clays could serve as practical adsorbents in the treatment of water and wastewater." They investigated the removal of eleven organic pollutants, including: butanol, hexanol, octanol, benzene, toluene, nitrobenzene, phenol, chloroform, dimethylphthalate, acetaldehyde and acetone; which were treated with organoclays created from the primary amines propylammonium (PA), dodecylammonium (DA) and dodecyldiammonium (DDA). Eight concentrations of each contaminant were prepared. X-ray diffraction studies of the various organoclays saturated with water and pollutants demonstrated "significant intercalcation" of the pollutant molecules between the clay platelets.

Five years later, Jaynes and Boyd's 1990 paper, “Trimethylammonium-Smectite as an Effective Adsorbent of Water Soluble Aromatic Hydrocarbons,” investigated the ability of trimethylphenylammonium (TMPA) and tetramethylammonium clays (TMA) to adsorb soluble hydrocarbons including benzene, toluene, ethylbenzene, p-xylene, butylbenzene and naphthalene. They were also able to construct adsorption isotherms for each contaminant and concluded that TMPA-smectite was potentially useful as a liner ingredient for petroleum storage facilities such as tank farms and underground storage tanks.

Their work also supported the leading hypothesis that describes how organoclays adsorb hydrocarbons - when large QACs are exchanged on montmorillonite; the organic cations form pillars that spread the clay platelets apart. The large interlamellar space allows for a hydrocarbon partition to form between the clay platelets. These changes in interlamellar distance have been measured by several authors using x-ray diffraction. Jaynes and Boyd also discovered that high cation-exchange montmorillonite may be less effective as a substrate than lower cation-exchange clay because the denser packing of QAC pillars between the clay plates may restrict the movement of aromatic molecules into the interlamellar space.
The term "isotherm" is used for convenience because the adsorption behavior of many organoclays follows a Langmuir isotherm, which was developed to describe the adsorption behavior of activated carbon. It assumes that there are a fixed number of adsorbent sites available on the surface and that adsorption is reversible. Unfortunately, the concept of an isotherm is misleading in its implication that the adsorptive properties of organoclay change with temperature or that the adsorption is reversible. Data which follows a Langmuir isotherm does not necessarily infer that the previously stated assumptions are valid.

Another 1990 paper, “Adsorption of Benzene, Toluene, and Xylene by two Tetramethyl-ammonium-Smectites Having Different Charge Densities” (Lee), also studied the adsorption of vapors and aqueous solutions of benzene, toluene, and xylene by several organoclays. They concluded that "low charge Wyoming TMA-smectite was very effective in removing benzene from water and may be a useful material for purifying benzene contaminated water."

In 1993 Zhang addressed some of the practical issues that needed to be resolved before organoclays could be recommended or manufactured for commercial water treatment. First, they investigated the factors that control the adsorption of organic cations on clays. It was determined that the smaller organic cations adsorb onto clays to a level exactly equal to the cation exchange capacity of the clays. They also discovered that large QACs (larger than 12 carbons) could possibly adsorb at nonexchangeable sites because they were able to exchange these materials at levels higher than cation exchange capacity. The degree to which QACs were adsorbed at nonexchangeable sites was directly related to the length of the alkyl chains of the amines.

Second, they discovered that more than 95% of the available sodium ions could be exchanged with QACs. Potassium, on the other hand, was replaced at only 70-75% of the sites. This indicates that sodium montmorillonite is the preferred raw material.

Finally, they conducted long-term desorption studies to discover if the sorption of organic cations was truly "permanent". They concluded that within their 180 days of investigation, the exchange was essentially irreversible. Further, they concluded that desorption did not increase with longer equilibrium time and found that the degree of desorption also decreased in inverse proportion to the length of the alkyl chains of the amines.

The 1993 study was followed by Kukkadapu and Boyd's 1995 study which prepared etramethylphosphonium (TMP)-clay and tetramethylammonium (TMA)-clay in order to study their ability to adsorb benzene, toluene and carbon tetrachloride vapor. Aqueous solutions of benzene, toluene, ethylbenzene, styrene, xylene and carbon tetrachloride were also studied. They also found that the adsorption of organic vapors by dry organoclay media was higher than in the aqueous solutions. The potential use of organoclay to adsorb organic vapors has apparently not been investigated further.
Finally, in 1996 Dentel created and evaluated organoclays made from trimethylammonium (TMA), hexadecyltrimethylammonium (HDTMA), and dioctadecyl-dimethylammonium (DDDMA). He noted that organoclay made from QACs containing small functional groups behave differently than those made from quaternary ammonium compounds containing larger functional groups (12-18 carbons). In the former case, adsorption is preferential or competitive and the magnitude of uptake is not dependent on the solubility of the organic solute. In the latter case, the magnitude of uptake is inversely proportional to the solute's water solubility and adsorption is not preferential or competitive. This latter behavior was observed in several of the case studies.

All of this exhaustive research and investigation can be summarized as follows:

• Many primary and quaternary amines are used as clay surface modifiers.
• All organoclays that have been studied will adsorb organic compounds to some degree.
• Of those clays that have been studied, several have been found to remove organic contamination from wastewater in potentially commercial quantities.
• The adsorption behavior of organoclay is fundamentally different from that of activated carbon. In certain circumstances, a hydrocarbon partition can be created between clay platelets. The generic term "sorption" is a more accurate description of the phenomenon.
• Adsorption and desorption tests have strongly suggested that commercial products should be manufactured from large molecular weight QACs. While this formulation hinders the adsorption of soluble hydrocarbons such as BTEX (Benzene, Toluene, Ethyl Benzene & Xylene), it is optimized for the removal of free and dispersed oil.

Information on Organoclays for Waste Stabilization

Surface modified clays (Organoclays) have found acceptance as components of sediment and soil stabilization admixtures, as components of permeable barriers and as adsorbents for hazardous oily & organic liquids.

Sediment stabilization consists of blending organoclay with the sediments of a river, lake or estuary in an effort to prevent leaching of contaminants, present in the groundwater, into the surface water.
Soil stabilization consists of adding a mixture of cement, fly ash, organoclay and powdered activated carbon with contaminated soil, which results in a matrix where the organic hydrocarbon contaminants are fixated and will not enter the aquifer below.

Permeable barriers are a concept that extends from sediments into slurry walls and landfill liners. The idea is to allow the water to pass through the barrier, be that groundwater or landfill leachate, but to intercept the contaminants, which are present in the plume.

Organoclays have also been repeatedly used to adsorb hazardous liquids in order to pass EPA 9095 (Paint Filter Test), EPA 9096 (Liquid Release Test) and in some cases to pass the EPA Toxic Characteristic Leachate Procedure (TCLP).

Organoclays & Radioactive Waste Stabilization

This process can be used to recover weapons grade materials as well as reprocessed Uranium from spent nuclear reactor fuel, and as such, its component chemicals are monitored. PUREX is an acronym standing for Plutonium and Uranium Recovery by EXtraction. The PUREX process is a liquid-liquid extraction method used to reprocess spent nuclear fuel, in order to extract uranium and plutonium, independent of each other, from the fission products.

http://en.wikipedia.org/wiki/PUREX

The liquid waste resulting from PUREX is a complex blend of organics and low viscosity oils with the following rough constituents:

Tributyl Phosphate                     17-20%

Aliphatic hydrocarbons (n-paraffin)
Undecane                      8-10%
Dodecane                      8-10%
Tridecane                      8-10%
Tetradecane                  8-10%

Aromatic hydrocarbons
Diethyl benzene             20-23%
Di-isopropyl benzene      20-23%

Aliphatic amine
Di-n-octylamine              6-10%

Final Specific Gravity                  0.80 to 0.95 g/cc

The Waste Lock® Organoclay BM-Qt-199 Granular has been tested successfully on surrogate PUREX waste from a major US Department of Energy site.  Contact us to see the full report (info@m2polymer.com)

Please contact M² Polymer Technologies directly with information on your particular waste stream so that an effective and appropriate adsorbent system can be designed to meet your needs.