Pyrolysis temperature affects biochar properties, which in turn determine its application potential. Here, we examined the properties of crofton weed biochar (C-BC) produced at different pyrolysis temperatures of 300°C, 400°C, 500°C, and 600°C. We measured the yield, ash content, pH, iodine sorption value (ISV), and elemental composition of C-BC. We also characterized C-BC using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared, as well as its ability to remove Pb²⁺ and Cd²⁺ from aqueous solution. C-BC yield decreased with increasing pyrolysis temperature, whereas ash content and pH increased. ISV first increased at 300–400°C and decreased at 500–600°C. For C-BC produced at pyrolysis temperatures 300–600°C (C-BC300 to C-BC600, respectively), H, N, and O content decreased, but C, Ca, Mg, P, and K content increased with increasing temperature. Water-soluble K⁺ content had the same trend as the K content, and water-soluble Ca²⁺, Mg²⁺, PO₄³⁻, NO₃⁻, and NH₄⁺ content decreased with increasing pyrolysis temperature. The (NO₃⁻+NH₄⁺), PO₄³⁻, and K⁺ content of C-BC was high, and the K⁺ content in C-BC600 was particularly high at up to 26,293.33 mg/kg. All C-BCs had a certain number of pore structures. Increasing pyrolysis temperatures decreased the amount of -OH, -COOH, aliphatic C-H, and polar C-O on the C-BC surface. As the pyrolysis temperature increased, calcium magnesium carbonate, calcium magnesium silicate, calcium magnesium phosphate, and potassium salt crystalline minerals gradually formed. The percentage of Pb²⁺ and Cd²⁺ removed increased with increasing pyrolysis temperatures. Overall, for C-BC, a low pyrolysis temperature was beneficial for producing a more porous biochar and increased content of water-soluble calcium, magnesium, nitrogen, and phosphorus, whereas high pyrolysis temperatures yield biochar that had high alkalinity, aromaticity, and stability, as well as heavy metal removal activity and water-soluble potassium content.

To provide the basic information about the release of heavy metals from the pyrite tailings of Huangjiagou pyrite mine, the pyrite tailings were investigated through a series of batch experiments under different initial pH of extractant, temperature, liquid-solid (LS) ratio, and soaking time conditions. Moreover, calcium carbonate was added in the pyrite tailings to determine the reduction effect on the release of heavy metals. The results show that Fe, Cr, Cu, Mn, Zn, and Ni were the major heavy metals in the pyrite tailings. Low initial pH and high LS ratio significantly promoted Fe, Cu, Mn, Ni, and Zn release, and high temperature significantly promoted Fe, Cu, Mn, and Ni release. Only small amounts of Cr were detected at low LS ratios. With the increase of soaking time, the released amount of Fe, Cu, Mn, Ni, and Zn increased to the maximum value within 48 h, respectively. After adding calcium carbonate, the released amounts of Fe, Cu, and Zn reduced at least 70.80% within 48 h soaking time. The results indicate that summer and the early soaking stage are the main phases for the release of heavy metals from the pyrite tailings. In the pyrite tailings, Cr is difficult to release. Adding calcium carbonate can effectively reduce the release of Fe, Cu, and Zn.

With the rapid development of industrialization, the amount of copper-containing wastewater is increasing, thereby posing a threat to the aquatic ecological environment and human health. Sludge biochar has received extensive concern in recent years due to its advantages of low cost and sustainability for the treatment of heavy-metal-containing wastewater. However, the heavy-metal-adsorption capacity of sludge biochar is limited. This study prepared a sodium pyrophosphate- (Na₄P₂O₇-) modified municipal sludge-based biochar (SP-SBC) and evaluated its adsorption performance for Cu(II). Results showed that SP-SBC had higher yield, ash content, pH, Na and P content, and surface roughness than original sewage sludge biochar (SBC). The Cu(II)-adsorption capacity of SP-SBC was 4.55 times than that of SBC at room temperature. For Cu(II) adsorption by SP-SBC, the kinetics and isotherms conformed to the pseudo-second-order model and the Langmuir–Freundlich model, respectively. The maximum adsorption capacity of SP-SBC was 38.49 mg·g⁻¹ at 35°C. Cu(II) adsorption by SP-SBC primarily involved ion exchange, electrostatic attraction, and precipitation. The desired adsorption performance for Cu(II) in the fixed-bed column experiment indicated that SP-SBC can be reused and had good application potential to treat copper-containing wastewater. Overall, this study provided a desirable sorbent (SP-SBC) for Cu(II) removal, as well as a new simple chemical-modification method for SBC to enhance Cu(II)-adsorption capacity.

To understand the effects of effective microorganisms (EMs) containing multiple strains on microbes and nutrients in kiwifruit planting soil, EMs prepared with four different strains were added to kiwifruit planting soil monthly from April to August. The counts of bacteria, fungi, actinomycetes, and total microbes were determined. The pH, total nitrogen (TN), alkali-hydrolyzable nitrogen (A-N), organic matter (OM), available potassium (A-K), and available phosphorus (A-P) of the soil were measured. Results indicated that the counts of bacteria, fungi, actinomycetes, and total microbes reached 60.33 × 10⁵, 4.00 × 10⁵, 0.92 × 10⁵, and 65.25 × 10⁵ CFU/g, respectively, in August, all of which were higher than those of the control group (CK). The bacterial count of the experimental group (EG) was higher than that of the CK in August. The pH-values of the EG were always lower than those of the CK. In August, the TN content of the EG was 1.52 g/kg, which was higher than that of the CK (1.35 g/kg). A significant negative association between the actinomycetes count and TN (p < 0.05) was found. For A-N and OM, the content of the EG (A-N, 125.18 mg/kg; OM, 49.84 mg/kg) was roughly the same as that of the CK (A-N, 112.51 mg/kg; OM, 53.11 mg/kg) in August. However, the A-K and A-P contents of the EG (A-K, 145.25 mg/kg; A-P, 111.25 mg/kg) were lower than those of the CK (A-K, 182.52 mg/kg; A-P, 202.19 mg/kg) in August. Results show that application of EMs in kiwifruit planting soil can increase the counts of soil microbes and might promote the absorption of major nutrients for kiwifruit tree.