Sorption of nonpolar aromatic contaminants by chlorosilane surface modified natural minerals

Our plain-English summary of Sorption of nonpolar aromatic contaminants by chlorosilane surface modified natural minerals, by P. Huttenloch, K.E. Roehl, K. Czurda (Environmental Science & Technology, 2001).

The study

• Authors: P. Huttenloch, K.E. Roehl, K. Czurda
• Journal: Environmental Science & Technology
• Published: 2001;35(21):4260-4
• Cited by: 25 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The efficacy of the surface modification of natural diatomite and zeolite material by chlorosilanes is demonstrated. Chlorosilanes used were trimethylchlorosilane (TMSCI), tert-butyldimethylchlorosilane (TBDMSCI), dimethyloctadecylchlorosilane (DMODSCI), and diphenyldichlorosilane (DPDSCI) possessing different headgroups and chemical properties. Silanol groups of the diatomite and zeolite were modified by chemical reaction with the chlorosilanes resulting in a stable covalent attachment of the organosilanes to the mineral surface. The alteration of surface properties of the modified material was proved by measurements of water adsorption capacity, total organic carbon (TOC) content, and thermoanalytical data. The surface modified material showed great stability even when exposed to extremes in ionic strength, pH, and to pure organic solvents. Sorption of toluene, o-xylene, and naphthalene from water was greatly enhanced by the surface modification compared to the untreated materials which showed no measurable sorption of these compounds. The enhanced sorption was dependent on the organic carbon content as well as on chemical characteristics of the chlorosilanes used. Batch sorption experiments showed that the phenyl headgroups of DPDSCI have the best affinity for aromatic compounds. Removal from an aqueous solution of 10 mg/L of naphthalene, o-xylene, and toluene was 71%, 60%, and 30% for surface modified diatomite and 51%, 30%, and 16% for modified clinoptilolite, respectively. Sorption data were well described by the Freundlich isotherm equation, which indicated physical adsorption onto the lipophilic surface rather than partitioning into the surface organic phase. The chlorosilane modified materials have an apparent potential for application in environmental technologies such as permeable reactive barriers (PRB) or wastewater treatment.

In plain English

This laboratory study from the University of Karlsruhe in Germany tested whether chemically treating two natural minerals, diatomite and a clinoptilolite-rich zeolite rock, with chlorosilanes would let them take up the aromatic pollutants toluene, o-xylene and naphthalene from water. The untreated minerals showed no measurable uptake of these compounds. Of the four chlorosilanes tried on diatomite, diphenyldichlorosilane (DPDSCl) worked best: it removed 56% of the naphthalene from a 10 mg/L solution, compared with 17% to 33% for the other three. For the later tests the DPDSCl treatment was made longer and repeated, and the methods state that the clinoptilolite was first converted by acid treatment and heating to an 'H-form'. Removal from 10 mg/L solutions of naphthalene, o-xylene and toluene was then 71%, 60% and 30% for the treated diatomite and 51%, 30% and 16% for the treated clinoptilolite. Uptake did not change significantly under extremes of pH or ionic strength (salt content). The authors concluded that, although more research is needed, these materials are potential sorbents for wastewater treatment or permeable reactive barriers. The article does not study asbestos or human health.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory materials experiment: chemical surface modification of minerals followed by batch sorption tests in water
• Who was studied: No people or animals were studied. The materials were a calcined diatomite from United Minerals (particle size 0.25-0.85 mm) and a clinoptilolite-rich tuff from Northern Carpathia (particle size 0.2-1.0 mm). Each was tested untreated and after surface modification.
• Exposure: There was no asbestos exposure. The minerals were treated with four chlorosilanes (TMSCl, TBDMSCl, DMODSCl and DPDSCl). For DPDSCl the reaction time was extended and the treatment repeated, and the clinoptilolite was first converted to the H-form by acid treatment. The materials were then exposed to water solutions of o-xylene (1-30 mg/L), toluene (1-100 mg/L) and naphthalene (1-20 mg/L).
• Main results:
  • Untreated diatomite and untreated clinoptilolite showed no affinity for toluene, o-xylene or naphthalene.
  • For diatomite, surface modification reduced water adsorption capacity from 120% (untreated) to zero with three of the chlorosilanes and to 9% with TMSCl. Naphthalene removal from a 10 mg/L solution was 20% with TMSCl, 17% with TBDMSCl, 33% with DMODSCl and 56% with DPDSCl. No naphthalene removal was detected with untreated diatomite.
  • DPDSCl-treated diatomite had a relatively low organic carbon content (1.6%), but its naphthalene sorption capacity was nearly double that of the other treatments.
  • Compared with a single 24 h treatment, double treatment with DPDSCl increased naphthalene sorption by 20% for diatomite and by 16% for clinoptilolite. Acid pretreatment (dealumination) of clinoptilolite improved sorption capacity by 29% relative to clinoptilolite without acid pretreatment.
  • Removal from 10 mg/L solutions of naphthalene, o-xylene and toluene was 71%, 60% and 30% for DPDSCl-modified diatomite and 51%, 30% and 16% for DPDSCl-modified clinoptilolite.
  • The modified materials showed no significant change in sorption under extremes of pH and ionic strength.
  • The sorption data fitted the nonlinear Freundlich equation. The authors interpreted this to mean the compounds most likely stuck physically to the diphenyl groups on the surface rather than dissolving into an organic phase.
• The authors' conclusion: The authors concluded that, although more research is needed, chlorosilane-modified clinoptilolite and diatomite are potential sorbents for aromatic organic compounds, for use in wastewater treatment or permeable reactive barriers.
• Limitations the authors state:
  • The authors state that more research is needed before these materials can be applied.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Amosite.

Medical terms in this study, explained in our Lexicon: Zeolite.

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