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Alkaline precipitation occurs when minerals such as calcium, aluminum, or magnesium combine with other minerals to form alkaline residues that are then emitted into the atmosphere, absorbed by water droplets in clouds, and then falls as rain.[1]
Natural causes[edit]
While most natural rains are weakly acidic, alkaline rain can also occur in natural conditions without the significant impact of pollutants.[2] Natural alkaline rains from semiarid areas carry a substantial amount of mineral dust lifted from the desert soil convection and transported by winds. Mixed with water vapor, they are carried by clouds and deposited to the ground in the form of rain dust.
Anthropogenic causes[edit]
The principal cause of alkaline rain are emissions from factories and waste deposits. Mineral dust containing large amounts of alkaline compounds such as calcium carbonate can also increase the pH of precipitation and contribute to basic rain.[3] Alkaline rain can be viewed as opposite to acid rain. Industrial processes such as coal combustion, limestone, chromium ore, alumina extraction, iron, and steel manufacture can cause pollution by producing alkaline residue.[1] These residues are significant and increasing in the global flux; these residues are composed of Na, CA or Mg oxides that are hydrated to produce soluble hydroxides.[1] Some other sources are from the surfaces of unpaved roads and soils that are covered in major alkaline elements Na, Mg, K and Ca.[4]
Impacts of alkalinity precipitation[edit]
Change in (pH 8.5-10) causes disturbances in ecosystems such as aquatic. The disturbance can alter the physiological changes to aquatic life, changing the rates at which they dispel ammonia which leads to accumulation in the organism.[1]The pH change in the water can cause precipitation of calcite from alkaline leachates that suffocate benthic and littoral aquatic habitats, along with reducing light penetration.[1]
Management[edit]
Air pollution control yields two management practices of recycling ceramic material or landfill after treatment.[1] These practices are made possible by several treatments methods of separation solidification/stabilization, thermal, and combined.[1] Most commonly used method for dealing with these types of waste such as bauxite is solidification / stabilization.[1] Remediation for alkaline leachate requires active aeration in order to promote carbonation, recirculation of drainage waters over stockpiled or lagooned residues, and acid dosing. Strong acids (HCl, H2SO4) are also used in neutralizing the pH; this is used at active processing plants but with this method, the liquid runoff can remain toxic to aquatic environments.[1] Wetlands are also a low-cost remedy for alkaline leachates.[1]
See also[edit]
References[edit]
- ^ a b c d e f g h i j k Gomes, Helena I.; Mayes, William M.; Rogerson, Mike; Stewart, Douglas I.; Burke, Ian T. (2016). "Alkaline residues and the environment: a review of impacts, management practices and opportunities". Journal of Cleaner Production. 112: 3571–3582. doi:10.1016/j.jclepro.2015.09.111. ISSN 0959-6526.
- ^ Zhang, D. D.; Peart, M. R.; Jim, C. Y.; Jia, La (2002-07-27). "Alkaline rains on the Tibetan Plateau and their implication for the original pH of natural rainfall". Journal of Geophysical Research: Atmospheres. 107 (D104): ACH 9.1–ACH 9.6. Bibcode:2002JGRD..107.4198Z. doi:10.1029/2001JD001332.
- ^ Özsoy, Türkan; Cemal Saydam, A (2000). "Acidic and alkaline precipitation in the Cilician Basin, north-eastern Mediterranean Sea". Science of the Total Environment. 253 (1–3): 93–109. Bibcode:2000ScTEn.253...93O. doi:10.1016/S0048-9697(00)00380-6. PMID 10843334.
- ^ Gatz, Donald F.; Barnard, William R.; Stensland, Gary J. (1986). "The role of alkaline materials in precipitation chemistry: A brief review of the issues". Water, Air, and Soil Pollution. 30 (1): 245–251. doi:10.1007/BF00305195. ISSN 1573-2932.