Asbestos cement waste treatment through mechanochemical process with KH2PO4 for its utilization in soil pH correction and nutrient delivery.

The manufacture of asbestos materials has been banished worldwide due to their toxicity, but discarding the existing wastes remains a challenge. We investigated an alternative mechanochemical method to treat asbestos-cement materials by loading them with potassium and phosphorus from KH2PO4 during the milling process to obtain a product used as liming and soil conditioner. The results showed total asbestos fibrous elimination after 7 to 8 h of milling. The materials showed a slow-release fertilizer profile. The liming property is maintained when the asbestos-cement weight proportion used is equal to or higher than KH2PO4. A comparative soil experiment with limestone also indicates that lower doses of the K- and P-enriched detoxified asbestos cement were required to reach similar liming effects. Maize cultivation (greenhouse) was used to evaluate its performance showing higher biomass production for the sample loaded with potassium and phosphorous.

Detoxification mechanism of asbestos materials by microwave treatment.

The detoxification mechanism of asbestos materials was investigated through simulations and experiments. The permittivities of pure CaO and Mg3Si4O12, as quasi-asbestos materials, were measured using the cavity perturbation method. The real and imaginary parts of the relative permittivity (ɛr' and ɛr″) of CaO are functions of temperature, and numerical simulations revealed the thermal distributions in an electromagnetic field with respect to both asbestos shape and material configuration based on permittivity. Optical microscopic observation revealed that the thickness of chrysotile fibers decreased as a result of CaO heating. The heating mechanism of asbestos materials has been determined using CaO phase, and the detoxification mechanism of asbestos materials was discussed based on the heating mechanism.

The interaction of asbestos and iron in lung tissue revealed by synchrotron-based scanning X-ray microscopy.

Asbestos is a potent carcinogen associated with malignant mesothelioma and lung cancer but its carcinogenic mechanisms are still poorly understood. Asbestos toxicity is ascribed to its particular physico-chemical characteristics, and one of them is the presence of and ability to adsorb iron, which may cause an alteration of iron homeostasis in the tissue. This observational study reports a combination of advanced synchrotron-based X-ray imaging and micro-spectroscopic methods that provide correlative morphological and chemical information for shedding light on iron mobilization features during asbestos permanence in lung tissue. The results show that the processes responsible for the unusual distribution of iron at different stages of interaction with the fibres also involve calcium, phosphorus and magnesium. It has been confirmed that the dominant iron form present in asbestos bodies is ferritin, while the concurrent presence of haematite suggests alteration of iron chemistry during asbestos body permanence.

Treatment and recycling of asbestos-cement containing waste.

The remediation of industrial buildings covered with asbestos-cement roofs is one of the most important issues in asbestos risk management. The relevant Italian Directives call for the above waste to be treated prior to disposal on landfill. Processes able to eliminate the hazard of these wastes are very attractive because the treated products can be recycled as mineral components in building materials. In this work, asbestos-cement waste is milled by means of a high energy ring mill for up to 4h. The very fine powders obtained at all milling times are characterized to check the mineralogical and morphological transformation of the asbestos phases. Specifically, after 120 min of milling, the disappearance of the chrysotile OH stretching modes at 3690 cm(-1), of the main crystalline chrysotile peaks and of the fibrous phase are detected by means of infrared spectroscopy and X-ray diffraction and scanning electron microscopy analyses, respectively. The hydraulic behavior of the milled powders in presence of lime is also tested at different times. The results of thermal analyses show that the endothermic effects associated to the neo-formed binding phases significantly increase with curing time. Furthermore, the technological efficacy of the recycling process is evaluated by preparing and testing hydraulic lime and milled powder-based mortars. The complete test set gives good results in terms of the hydration kinetics and mechanical properties of the building materials studied. In fact, values of reacted lime around 40% and values of compressive strength in the range of 2.17 and 2.29 MPa, are measured.

Counting rules for estimating concentrations of long asbestos fibers.

Mounting evidence that long asbestos fibers (e.g. >20 or even 40 µm) pose the greatest cancer risk underscores the need for accurate measurement of concentrations of such fibers. These fiber lengths are of the same order of magnitude as the size of openings in the grids (typically ≈90 µm per side) used to analyze asbestos samples by transmission electron microscopy. This means that a substantial proportion of long fibers will cross the edge of a grid opening (GO) and therefore not be completely visible. Counting rules generally deal with such fibers by assigning a length equal to twice the visible length. Using both theoretical and simulation methods, we show that this doubling rule introduces bias into estimates of fiber concentrations and the amount of bias increases with fiber length. We investigate an alternative counting rule that counts only fibers that lie completely within a GO and weights those fibers by the reciprocal of the probability that a fiber of that length lies totally within a GO. This approach does not have the bias inherent in the doubling rule and is essentially unbiased if the stopping rule specifies a fixed number of GOs to be scanned. However, a stopping rule based on successively scanning GOs until a fixed number of fibers have been counted will introduce bias into any counting method, although this bias may typically not be large enough to be of practical concern. We recommend use of the weighted approach as a supplement to use of the doubling rule when estimating concentrations of long fibers, irrespective of the stopping rule employed.