Comparisons of pollution characteristics, emission situations, and mass loads for heavy metals in the manures of different livestock and poultry in China.

The application of livestock and poultry manures was the predominant source of heavy metals in agricultural soils, particularly in China. It is important to systematically compare the pollution characteristics, emission situations and mass loads for heavy metals in the manures of different livestock and poultry in China. According to analysis and estimation based on the reported concentration levels of eight heavy metals (Zn, Cu, Pb, Cd, Cr, Hg, As, and Ni) and the feed quantities of livestock (pig, cattle, and sheep) and poultry in 2017, the concentrations of Zn and Cu and the over-standard frequencies of Zn, Cu, Cd, and As were much higher than those of other heavy metals, especially in pig manure. In 2017, the total emission of livestock and poultry manure in China was 1.64 × 109 t (FW), which was mainly excreted from cattle (45.77%); while the total emission of heavy metals sourced from manures was 2.86 × 105 t (DW), with the predominant contribution originating from pig manure (71.52%). The highest mass loads of manures and heavy metals were observed in Shandong, Tianjin, Henan, and Shanghai, where heavy metal contamination may be occurring (especially for Zn and Cu). The heavy metal concentrations in livestock and poultry manures of China were similar to other countries; however, more heavy metals were discharged into agricultural land through manure (especially for Zn and Cu). For many countries, abundant Zn and Cu exist in agricultural soils, principally contributed by livestock and poultry manures. These heavy metals originate from their addition to livestock and poultry feeds. Therefore, reducing the addition of Zn and Cu in feeds is an effective measure to lower their input into agricultural soils.

Modified granulation of red mud by weak gelling and its application to stabilization of Pb.

This study presents a novel modification of red mud (RM) with cementitious materials by rotary drum granulation under partial hydration. Admixtures and surfactants were applied to improve the microspore structure of red mud-based granules in order to stabilize Pb steadily. Through XRD and SEM-EDS analyses, it was demonstrated that calcite, the main alkali in RM, was partially concreted and coated. Compared to pH 12.47 for RM, the lowest pH of the granules was 10.66 implying that the release of OH(-) from hydrolysis and decomposition was decreased. Based on stabilization of Pb, influence on soil properties and forming qualities, composition of the optimum granule PSP was determined as 5% cement, 5% gypsum, 1% rice straw, and 0.1% emulsifier OP-10. Within a 90 d remediation, immobilization of ionic Pb in a 500 mg kg(-1) Pb-contaminated artificial soil was 9.85 mg kg(-1) at day 30 with 5% PSP2 as substitute. Furthermore, the reverse increase diminished as the final concentration was 11.13 mg kg(-1) while it was 14.25 mg kg(-1) by RM. The increase of residual Pb was 122.61%, which was better than the 83.92% of RM. Particularly, the highest pH in mine soil was 11.09 at day 1 with RM, but the decrease of ionic Pb was 46.26%. Meanwhile, a significant deviation from the control soil zeta-potential lasted longer and the recovery was more difficult, as compared to the granules. Therefore, a granulated modification of RM is shown to be very important when aiming at steady release of OH(-) to improve the later stabilization of Pb.