No Foul, No Harm

Experiments test organoclay's sorptive capacity

• By George R. Alther
• Mar 01, 2007

While cationic and anionic resins typically last a long time in industrial wastewater and groundwater applications, they frequently become fouled by any of several compounds. The fouling eventually will destroy the resins' capacity to adsorb metals or other materials.

Plant operators often manage this problem by using additional regenerant chemicals and rinse water, which translates into higher management and labor costs. A more economical solution is to pre-polish the waste stream with organically modified clay.

Pre-polishing Makes a Difference
Activated carbon or membranes can be used in pre-polishing, but both are quickly blinded by oil. The fouling problem is transferred from the resin to the carbon or membrane. If sacrificial resin is used to trap the oil, it would have to be anionic, which can be costly.

Organically modified clay, or organoclay, is used in groundwater remediation to remove 50 percent of its weight in oil. The technology used for pre-polishing wastewater to protect the integrity of the ion exchange resin and membranes is the same as for groundwater treatment.

This article presents results from two column experiments on the sorptive capacity of organoclay/anthracite, a non-polar organoclay and activated carbon, to an aqueous-oil solution. The organoclay is blended with anthracite to prevent early plugging of the pore spaces between the granules. A 13-inch long by 1.5-inch diameter column was constructed from polyvinyl chloride and filled with the sorbent material. A peristaltic pump forced an aqueous-metal solution (containing 1,200 milligrams per liter mg/L vegetable oil) up through the column to displace void-space air and ensure maximum contact with the sorbent material. Using chemical oxygen demand analysis, the researcher analyzed periodic samples for organic composition (see Tables 1, 2, and Figure 1).

Figure 1 shows the breakthrough curve of oil through a column of organoclay/anthracite. Normalized concentration is defined as the oil concentration in the effluent divided by the concentration in the influent stream. Pore volume is the volume of water that occupies the total pore space inside the packed column. This graph can be used to determine the pore volume associated with a selected removal efficiency. Pore volume data can be used to calculate the quantity of organoclay required in a specific application.

Depending on the solubility of the oil, organoclay may be used alone or followed by activated carbon to reduce the oil content to a non-detectable level. The carbon also removes chlorine.

The Exchange
Organoclays are bentonites that have been chemically modified with quaternary amines, which render the bentonite hydrophobic or organophylic. Bentonites consist primarily of montmorillonite-type clay. They are a natural cation exchange resin; the exchangeable ions being primarily sodium, calcium, and magnesium. These ions are exchanged with the nitrogen end of the quaternary amine.

In granular form, organoclays can be placed into the same filter vessels as activated carbon. Once immersed in water, the quaternary amine chains will stand up perpendicular to the clay platelets. As an oil droplet encounters the amine, the amine will partition into that droplet and fixate it by coulombic forces, permanently removing the oil. In this fashion, and by anion exchange, they also remove humic acids, polychlorinated biphenyls, other chlorinated hydrocarbons, and any organic associated with oil. Only anionic and non-ionic surfactants can remove the oil once it is attached to the organoclay.

This article also presents data summarizing the results from five sets of column experiments on the sorptive capacity of TC-75 (16 x 40 mesh), a cationic organoclay, to aqueous solutions of five different organic acids. A 30-inch long by 3-inch diameter column was constructed from polyvinyl chloride and filled with the sorbent material. A peristaltic pump forced an aqueous solution containing between 700 mg/L and 1,200 mg/L of organic acid up through the column to displace void-space air and ensure maximum contact with the sorbent material. Using a spectrophotometric method, the researcher analyzed samples collected periodically at the column outflow.

The regeneration process used in some experiments consisted of filling the column overnight with a solution of 3 percent sodium chloride and 1 percent sodium hydroxide. After that, the column was rinsed with tap water for 5 minutes before feeding it again with the aqueous-organic-acid solution (see Tables 3 to 10, Figures 2 to 5). This type of cationic organoclay can be regenerated onsite several times like ion exchange resins.

In Figure 2, bed volume is the total volume of the empty column and is an indication of the total volume of influent treated for a specific removal efficiency (normalized concentration). Note that the efficiency is lower for regenerated clay versus fresh clay.

Experiment results for sorption of organoclay/anthracite and activated carbon.

Table 1. Sorbent mass, porosity, flow rate, and residence time information for organoclay/anthracite and activated carbon sorbent column experiments. Sorbent Mass sorbent Porosity Flow rate Residence (kg) (lb) (mL/min) (gal/hr) (min) Organoclay/anthracite 0.138 0.30 0.31 14.5 0.24 8.01 Activated carbon 0.098 0.20 0.31 16.4 0.26 7.08 Table 2. Ninety-five percent breakthrough for organoclay/anthracite and activated carbon sorbent materials given in pore volumes (PV) and minutes along with estimated mass of oil sorbed per mass of sorbent. Sorbent Breakthrough Mass Sorbed Mass sorbed / mass sorbent (PV) (min) (kg) (lb) (g/kg) (lb/lb) (% by sorbent) Organoclay/anthracite 1150 9200 65.8 0.14 477 0.48 47.7 Activated carbon 167 1182 9.4 0.021 96 0.09 9.6 Figure 1. Breakthrough curve of oil through a column of organoclay/anthracite and activated carbon

Experiment results for sorption of tannic acid (Aldrich) on TC-75 16x40 with column regeneration.

Table 3. Sorbent mass, porosity, flow rate, and residence time information for TC-75 16x40 sorbent column experiments. Sorbent Mass sorbent Porosity Flow Rate Residence (kg) (lb) (mL / min) (gal / hr) (min) TC-75 16x40 2.1 4.6 0.3 48 0.76 21 Table 4. Ninety-five percent breakthrough for TC-75 16x40 sorbent given in bed volumes (BV) and minutes along with estimated mass of tannic acid sorbed per mass of sorbent. Sorbent Breakthrough Mass Sorbed Mass sorbed / mass sorbent (BV) (min) (kg) (lb) (mg/kg) (lb/lb) (% by sorbent) Before regeneration 32 2180 41300 0.091 19667 0.0197 1.97 After regeneration 20 1360 30499 0.067 14523 0.0145 1.45 Total 52 3540 71799 0.158 34190 0.0342 3.42 Figure 2. Breakthrough curve of tannic acid through a column of TC-75 16x40

Experiment results for the sorption of fulvic acid (Horizon) to TC-75 16x40 with column regeneration.

Table 5. Sorbent mass, porosity, flow rate, and residence time information for TC-75 16x40 column experiments. Sorbent Mass sorbent Porosity Flow Rate Residence (kg) (lb) (mL / min) (gal / hr) (min) TC-75 16x40 2.91 6.4 0.21 60 0.95 20 Table 6. Ninety-five percent breakthrough for TC-75 16x40 sorbent given in bed volumes (BV) and minutes along with estimated mass of fulvic acid sorbed per mass of sorbent. Sorbent Breakthrough Mass Sorbed Mass sorbed / mass sorbent (BV) (min) (kg) (lb) (mg/kg) (lb/lb) (% by sorbent) Before regeneration 45 4440 42373 0.093 14561 0.0146 1.46 After regeneration 27 2720 21410 0.047 7357 0.0074 0.74 After second regeneration 22 2000 16424 0.036 5644 0.0056 0.56 Total 94 9160 80207 0.176 27563 0.0276 2.76 Figure 3. Breakthrough curve of fulvic acid through a column of TC-75 16x40

Experiment results for the sorption of humic acid (Aldrich) on TC-75 16x40

Table 7. Sorbent mass, porosity, flow rate, and residence time information for TC-75 16x40 sorbent column experiments. Sorbent Mass sorbent Porosity Flow Rate Residence (kg) (lb) (mL / min) (gal / hr) (min) TC-75 16x40 2.1 4.6 0.28 60.1 0.95 20 Table 8. Ninety-five percent breakthrough for TC-75 16x40 sorbent given in bed volumes (BV) and minutes along with estimated mass of tannic acid sorbed per mass of sorbent. Sorbent Breakthrough Mass Sorbed Mass sorbed / mass sorbent (BV) (min) (kg) (lb) (mg/kg) (lb/lb) (% by sorbent) Before regeneration 107 7700 61475 0.135 29274 0.0293 2.93 After regeneration 79 5700 40573 0.089 19320 0.0193 1.93 Total 186 13400 102048 0.225 48594 0.0486 4.86 Figure 4. Breakthrough curve of humic acid through a column of TC-75 16x40

Experiment results investigating the sorption of Quantum H (Horizon) to TC-75 16x40

Table 9. Sorbent mass, porosity, flow rate, and residence time information for TC-75 16x40 sorbent column experiments. Sorbent Mass sorbent Porosity Flow Rate Residence (kg) (lb) (mL / min) (gal / hr) (min) TC-75 16x40 2.81 6.2 0.28 155 2.46 5.8 Table 10. Ninety-five percent breakthrough for TC-75 16x40 sorbent given in bed volumes (BV) and minutes along with estimated mass of Quantum Humic acid sorbed per mass of sorbent. Sorbent Breakthrough Mass Sorbed Mass sorbed / mass sorbent (BV) (min) (kg) (lb) (mg/kg) (lb/lb) (% by sorbent) TC-75 16x40 364 2111 106201 0.234 37794 0.0378 3.78 Figure 5. Breakthrough curve of Quantum H through a column of TC-75 16x40

This article originally appeared in the 03/01/2007 issue of Environmental Protection.