Magnetically modified spent coffee grounds for dyes removal

Large amounts of spent coffee grounds are discharged from food industries, for example, during the instant coffee manufacture. Although part of them is reused as compost and animal feed, most of the coffee grounds are burned as a waste. However, this material can be used as a biosorbent for xenobiotics removal. Spent coffee grounds were magnetically modified by contact with water-based magnetic fluid. This new type of magnetically responsive biocomposite materials can be easily separated by means of commercially available magnetic separators or strong permanent magnets. Magnetic coffee grounds can be used as an inexpensive magnetic adsorbent for the removal of water-soluble dyes. Seven dyes (crystal violet, malachite green, amido black 10B, Congo red, Bismarck brown Y, acridine orange and safranin O) were used to study the adsorption process. The dyes adsorption could be described with the Langmuir isotherm. The maximum adsorption capacities reached the value 73.4 mg of dye per g of dried magnetically modified coffee grounds for acridine orange; it corresponds to 276.6 mu mol g(-1). This adsorbent can also be used for magnetic solid-phase extraction of crystal violet from extremely diluted solutions. To conclude, magnetic modification of spent coffee grounds resulted in the formation of a new, promising adsorbent for selected xenobiotics removal.