ES2282056A1 - Sludge utilization for heavy metal elimination in watery dissolution, involves sludge recycling, where sludge is generated during manufacture of pressed paper with dry content in organic form of thirty five point two percent cellulose fiber - Google Patents

Abstract

The utilization involves recycling sludge, coming from recycled paper. The sludge is generated during the manufacture of paper presses and has a dry content in an organic form of thirty five point two percent cellulose fiber. The remaining material is calcium carbonate. The pyrolysis of the sludge is effective for the heavy metal elimination e.g. copper, nickel, cadmium, zinc, lead and chromium of contaminated water in different concentrations.

Description

Use of waste sludge from of the paper industry for heavy metal removal in aqueous solution

Sector of the technique to which the invention relates

The technical sector in which the Present invention is environmental engineering. Plus specifically it consists in the development of valorization techniques of the dewatering sludge produced in the manufacturing process of newsprint from recycled paper, through its transformation into a carbon adsorbent and subsequent use of this adsorbent in water treatment contaminated by metals, specifically Cu, Ni, Cd, Zn, Pb and Cr.

Statement of prior art

Paper consumption in Spain in 2005 amounted to 7.2 million tons / year being the consumption per 170 kg capita. In addition, in Spain there are more than 130 factories pulp and paper producers with an annual turnover of 4,000 millions of euros. In fact, the paper industry is expected increase its production by more than 1 million tons in the next years which would mean an increase of 19% over the current production. This situation can cause the production of waste from the paper industry increases considerably. By it is necessary to look for the best available techniques to minimize waste production in this sector.

The first objective of all waste management It is the minimization of them. Secondly it should be encouraged Recycling and reuse of waste. However, in those cases in which the latter is not possible should be designed New processes for the recovery of waste. In this sense, thermochemical methods (combustion, gasification or pyrolysis) they are applicable when it comes to valorising or treating waste with a high organic matter content, as is the case with the sludge of destined from paper recycling.

Waste pyrolysis consists of heat treatment thereof in an inert atmosphere, to temperatures between 300-700 ° C. During this treatment three fractions are generated: solid, Liquid and gaseous. The liquid and gas fractions could be used as fuels due to its high calorific value. Refering to solid fraction, in recent years its use as low price active carbon.

Active carbons are carbonaceous materials with a high porosity and high specific surface area that is the responsible for its high adsorption capacity. This ability to adsorption is also influenced by the presence of groups functional (carbonyls, ketones, lactones, phenols, ethers, etc.) on the surface of the coal. Virtually any substance with a high carbon content can be a potential source of active carbon Approximately 35% of active carbon is obtained at from mineral coal and another 35% of wood in general.

Traditionally, active coals commercials have been used for the removal of compounds organic in aqueous and gaseous media. However, its high price Limit your interesting applications. The preparation of coals assets from waste, although it generates materials with less adsorbent capacity, is presented as an interesting alternative since it involves the recovery of a waste and its possible use in the waste generating facilities themselves.

The preparation of active carbon depends on the starting material but in general the following are distinguished phases:

?

Grinding of the starting material for the selection of the appropriate grain size.

?

Pyrolysis

?

Physical or chemical activation with in order to increase the specific surface of the carbonaceous material. The term "physical activation" is used when activation it is carried out with gaseous compounds (CO2, water vapor, air). On the other hand, "chemical activation" consists of precursor pretreatment with chemical compounds such as H 3 PO 4, H 2 SO 4 or ZnCl 2.

One of the main problems Today's environmental is the presence of metals in the means, medium. Unlike organic compounds, metals do not they can be destroyed so they become persistent waste in the environment. On the other hand, its easy leaching in media Aqueous acids makes it difficult to deposit and allows their mobilization. Industrial activities such as metallurgy, mining, manufacture of dyes, pigments, paper pulp or fertilizers, coal combustion or oil refineries produce significant amounts of metals and compounds daily metallic that are dumped directly or indirectly into water. These Polluted waters pose a dangerous threat to man. According to the State Register of Emissions and Pollutant Sources, in In 2004, 2.15 t of Cu, 4.07 t were poured directly into the water of Ni direct and 3.44 t indirect or 22 t direct of Zn.

The technologies for the treatment of these waters contaminated with metals are based primarily on physicochemical treatments of neutralization, precipitation, decantation, flotation, phonic exchange, filtration, etc. Sayings treatments are usually expensive and inefficient, since, frequently, they give rise to dangerous by-products or waste also pollutants that must be taken to the landfill. In the In recent years, various studies focus on the elimination of metals by adsorption processes in commercial active carbons, that have the disadvantage of being very expensive or adsorbents of carbon obtained from waste after a pyrolysis process and physical or chemical activation.

The present invention is an important advance because it allows the removal of water metals contaminated by carbon adsorbents prepared from sludge after a simple pyrolysis process at 650ºC for 2 hours When an activation process is not performed post-pyrolysis reduces the cost of the process of preparation although the specific surface of the prepared material She's not really tall. However, the results obtained show high metal removal rates, greater than 65% by weight in many cases, so these carbon adsorbents are they could use in the paper industry itself or in others industries that wastewater with a high metal content.

Explanation of the invention.

Characterization physicochemical of the dewatering sludge produced in the process of manufacturing press paper from paper recycled shows that it is a residue with a content of organic matter greater than 35.2%, mostly fibers of cellulose (highly porous plant material) with a fiber size homogeneous The dewatering sludge considered herein The invention also has organic compounds used in production processes of recycled paper (H 3 PO 4), H 2 O 2, aluminum polychloride, anionic polyacrylamide, urea, etc.) Heavy metals are also concentrated in the mud (such as Ni, Zn, Pb, Cr, Cd, As, etc.), although its concentration is so low that its use is authorized as an organic amendment of floors.

The main objective is the elimination of metals (Cu, Ni, Cd, Zn, Pb and Cr) in aqueous solution by means of a carbon adsorbent characterized in that the adsorbent is prepared from a dewatering sludge from the paper industry.

For this the following is followed process:

?

Heat treatment of mud destined, at a temperature between 500 and 650ºC and for a period between 1.5 and 2.5 hours, to obtain the carbon adsorbent, a material with a carbon content not less than 25.5% by weight, basic pH (between 10 and 11), surface BET (parameter indicative of the specific surface of the material) greater than 125 m2 / g and a cation exchange capacity greater than 11 cmol (+) / kg.

?

Carbon Adsorbent Blend with the aqueous pH solution between 3 and 5 with a metal concentration (Cu, Ni, Cd, Zn, Pb or Cr) between  10 and 200 mgL -1.

?

Filtration of the mixture for separate the carbon adsorbent from the solution.

The performance of the pyrolysis process is 57.9% by weight.

To check the possible use of the material thus prepared in water purification studies the removal of Cu, Ni, Cd, Zn, Pb and Cr in aqueous solution. The experiments are performed at acidic pH (pH = 3 and pH = 5) to avoid metal precipitation

The following table shows the percentages of elimination obtained for the different metals. The results show how the prepared adsorbent is effective in eliminating heavy metals such as Cu, Ni, Cd, Zn, Pb and Cr of contaminated water in different concentrations, obtaining the best results for pH 5. In fact, for Cr, percentages of 100% removal for almost all concentrations rehearsed

one

Detailed exposition of an embodiment of the invention

The sludge is dried at room temperature until eliminate most of the water it contains due to its process of obtaining. A material with a content in humidity of 2.8% by weight.

Once dry, the mud is milled and sieved until achieve a particle size of less than 2 mm in diameter. For the heat treatment is selected 100 g of sample that introduced into a cylindrical reactor of 2 L volume. Said reactor it is closed and a flow of N 2 of 10 mLmin -1 is passed in order to achieve an inert atmosphere inside. Subsequently, it undergoes a heat treatment with a speed heating of 3ºCmin -1 to reach 650ºC. Bliss temperature is maintained for 2 hours.

The metal removal experiments (Cu, Ni, Cd, Zn, Pb and Cr in aqueous solution) are performed as follows mode. First, different solutions are prepared for each metal with metal concentrations of 10, 25, 50, 100, 150 and 200 mg L -1. The experiments are carried out at two different acidic pHs (3 and 5). In each experiment 20 mL of solution is mixed with 50 mg of adsorbent in an erlenmeyer flask. Subsequently, the mixture is stir at 500 rpm, at room temperature, for a time of 2 hours and then filtered. The metallic content of the Dissolution is measured by atomic absorption spectrometry.

Claims (2)

1. Use of dewatering sludge from the paper industry for metal disposal heavy in aqueous solution, preparing the sludge previously through the following stages:

?

Heat treatment of mud destined, at a temperature between 500 and 650ºC and for a period between 1.5 and 2.5 hours, to obtain the carbon adsorbent, a material with a carbon content not less than 25.5% by weight, basic pH (between 10 and 11), surface BET (parameter indicative of the specific surface of the material) greater than 125 m2 / g and a cation exchange capacity greater than 11 cmol (+) / kg.

?

Carbon Adsorbent Blend with the aqueous pH solution between 3 and 5 with a metal concentration (Cu, Ni, Cd, Zn, Pb or Cr) between  10 and 200 mgL -1.

?

Filtration of the mixture for separate the carbon adsorbent from the solution.

2. Use of dewatering sludge from the paper industry for metal disposal heavy in aqueous solution according to claim 1 wherein the heavy metal concentrations in aqueous solutions they are comprised between 10 and 200 mgL -1.