Different Response to Cd2+ Adsorption by Alkali-modified Biochars Derived From Soybean Straw and Rape Straw

Biochars have been modified by alkali (Ca(OH)2) to enhance Cd sorption capacity in aqueous solution. In this research, the alkali-modified (Ca) biochars were prepared by co-pyrolyzing lime (Ca(OH)2) and soybean straw (SBB) or rape straw (RSB) at 450 °C. The absorption mechanism was investigated by a series of experiments and was provided by quantitative analysis. The maximum adsorption capacities of Cd2+ by Ca-SBB and Ca-RSB were calculated to be 78.49 mg g−1 and 49.96 mg g−1, which were 1.56 and 1.48 times higher than SBB (50.40 mg g−1) and RSB (33.79 mg g−1), respectively. Compared with the original biochar (SBB, RSB), alkali-modified biochars (Ca-SBB and Ca-RSB) were found to have faster adsorption kinetics and lower desorption efficiencies. The mechanism study indicated that Ca(OH)2 modification effectively enhanced the contribution of ion exchange and decreased the contribution of functional groups complexation. After Ca(OH)2 modification, precipitation and ion exchange mechanisms dominated Cd2 + absorption on Ca-SBB, accounting for 49.85% and 34.94% of the total adsorption, respectively. Similarily ion exchange and precipitation were the main adsorption mechanism on Ca-RSB, accounting however for 61.91% and 18.47% of total adsorption, respectively. These results suggested that alkali-modified biochars have great potential in adsorbing cadmium in wastewater.

Selected Properties of Formaldehyde-Free Polymer-Straw Boards Made from Different Types of Thermoplastics and Different Kinds of Straw

This research investigated the effects of different thermoplastics types and different kinds of straw on selected properties of polymer-straw boards. Polyethylene, polyethylene, and polystyrene of virgin and of recycled origin were used for bonding the boards. Three kinds of straw were used: rape (Brassica napus L. var. napus), triticale (Triticosecale Witt b m.), and rye (Secale L.). Five-layer polymer-straw boards were produced. The obtained boards differed in both the materials they were made of and the moisture content (7, 25, and 2% for the core, the middle, and the face layers, respectively), and 30% of straw particles were substituted with thermoplastics added to the face layers. It was found that properties of polymer-straw boards strongly depend on both the kind of straw and the type of polymer used. The best mechanical properties were obtained for rye straw and polystyrene or recycled polymers, whereas the best hydrophobic properties were observed for rape straw combined with recycled polyethylene or polypropylene. Although recycled polymers improved the hydrophobic properties of the boards, they impaired their mechanical properties in comparison with the reference ones. However, in terms of bending strength, they still met the requirements for heavy duty load-bearing boards for use in humid conditions (20 MPa for P7 boards according to EN 312).

Fabrication of three bio-adsorbents from different parts of rape straw

In this paper, three kinds of bio-adsorbents are fabricated from the different parts of rape straw, which are adsorbent-core, adsorbent-hull, and adsorbent-stalk, respectively. As the adsorbates, kerosene, paraffin, rapeseed oil and dibutyl phthalate are employed to evaluate the adsorption performance of the three kinds of bio-adsorbents. The results suggest that the three bio-adsorbents exhibit very different adsorption properties. The bio-adsorbent of adsorbent-core has much higher adsorption quantity to all of the four adsorbates than the other two bio-adsorbents. The adsorption mechanism of the three bio-adsorbents is investigated. The results illustrate that different bio-adsorbents own different micro-morphologies. The special micro-chamber structure is found in bio-adsorbent of adsorbent-core, which is seen as the main reason of owning excellent adsorption performance. The adsorption volume of unit mass (Va) was proposed to evaluate the intrinsic adsorption properties of the bio-adsorbents. The recovery performance of the bio-adsorbents by using of two different treatment methods is investigated. The effect of treatment on recovery rate is discussed.